第九组IsHistoryRepeatingItself详解

ESCAPING NASH INFLATIONIN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENTA BSTRACT.Mean dynamics describe the convergence to self-confirming equilibria of self-referential systems under discounted least squares learning.Escape dynamics recurrentlypropel away from a self-confirming equilibrium.In a model with a unique self-confirmingequilibrium,the escape dynamics make the government discover too strong a version ofthe natural rate hypothesis.The escape route dynamics cause recurrent outcomes close tothe Ramsey(commitment)inflation rate in a model with an adaptive government.Key Words:Self-confirming equilibrium,mean dynamics,escape route,large deviation,natural rate of unemployment,adaptation,experimenta-tion trap.‘If an unlikely event occurs,it is very likely to occur in the most likely way.’Michael Harrison1.I NTRODUCTIONBuilding on work by Sims(1988)and Chung(1990),Sargent(1999)showed how a government adaptivelyfitting an approximating Phillips curve model recurrently sets inflation near the optimal time-inconsistent ouctome,although later inflation creeps back to the time-consistent suboptimal outcome of Kydland and Prescott(1977).The good outcomes emerge when the government temporarily learns the natural rate hypothe-sis.The temporary escapes from the time-consistent outcome symptomize a remarkable type of escape dynamics that promote experimentation and that are induced by unusual shock patterns that interact with the government’s adaptive algorithm and its imperfect model.The escapes lead to dramatic changes in the government’s inflation policy as it temporarily overcomes its inflationary bias.Some simulated time paths of inflation for different specifications of the model are shown in Figure1.Inflation starts and remains near the high time-consistent value for a while,is rapidly cut to zero,but then gradually2IN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENTF IGURE ofthe model.approaches the time-consistent high value again.This paper explains the dynamic forces that drive these outcomes.Escape dynamics from self-confirming equilibria can occur in a variety of models with large agents who use adaptive algorithms to estimate approximating models.1For con-creteness,this paper focuses on the Phillips curve model studied by Sargent(1999).The model has the following features:(1)the monetary authority controls the inflation rate, apart from a random disturbance;(2)the true data generating mechanism embodies a version of the natural rate hypothesis in an expectational Phillips curve;(3)as in Kydland and Prescott(1977),a purposeful government dislikes inflation and unemployment and a private sector forecasts inflation optimally;but(4)the monetary policy makers don’t know the true data generating mechanism and instead use a goodfitting approximating model.The fundamentals in the economy arefixed,including the true data generating mechanism,preferences,and agents’methods for constructing behavior rules.Changes in the government’s beliefs about the Phillips curve,and how it approximates the natural rate hypothesis,drive the inflation rate.Inspired by econometric work about approximat-ing models by Sims(1972)and White(1982),we endow the monetary authority,not with the correct model,but with an approximating model that it nevertheless estimates with good econometric procedures.We use the concept of a self-confirming equilibrium,a natural equilibrium concept for behavior induced by an approximating model.2In a self-confirming equilibrium,beliefs are correct about events that occur with positive probability in equilibrium.The approxi-mating model is‘wrong’only in its description of events that occur with zero probability in equilibrium.Among the objects determined by a self-confirming equilibrium are theESCAPING NASH INFLATION3 parameters of the government’s approximating model.While the self-confirming equi-librium concept differs formally from a Nash(or time consistent)equilibrium,3it turns out that the self-confirming equilibrium outcomes are the time-consistent ones.Thus,the suboptimal time consistent outcome continues to be our benchmark.Like a Nash equilibrium,a self-confirming equilibrium restricts population objects (mathematical expectations,not sample means).We add adaptation by requiring the government to estimate its model from historical data in real time.We form an adap-tive model by having the monetary authority adjust its behavior rule in light of the latest model estimates.Thus,we attribute‘anticipated utility’behavior(see Kreps(1998))to the monetary authority.Following Sims(1988),we study a‘constant gain’estimation al-gorithm that discounts past observations.Called a‘tracking algorithm’,it is useful when parameter drift is suspected(see e.g.Marcet and Nicolini(1997)).Results from the literature on least squares learning(e.g.,Marcet and Sargent(1989a), Woodford(1990),Evans and Honkapohja(1998))apply and take us part way,but only part way,to our goal of characterizing the dynamics of the adaptive system.That litera-ture shows how the limiting behavior of systems with least squares learning is described by an ordinary differential equation called the‘mean dynamics’.They describe the(un-conditionally)average path of the government’s beliefs,in a sense that we shall describe precisely.For our model,the mean dynamics converge to the self-confirming equilibrium and the time consistent outcome.Thus,the mean dynamics do not account for the recur-rent stabilizations in the simulations of Sims(1988),Chung(1990),and Sargent(1999). We show that these stabilizations are governed by another deterministic component of the dynamics,described by another ODE,the‘escape’dynamics.They point away from the self-confirming equilibrium and toward the Ramsey(or optimal-under-commitment) equilibrium outcome.So two sorts of dynamics dominate the behavior of the adaptive system.(1)The mean dynamics come from an unconditional moment condition,the least squaresnormal equations.These dynamics drive the system toward a self-confirmingequilibrium.4(2)The escape route dynamics propel the system away from a self-confirming equilib-rium.They emerge from the same least squares moment conditions,but they areconditioned on a particular“most likely”unusual event,defined in terms of the disturbance sequence.This most likely unusual event is endogenous.The escape route dynamics have a compelling behavioral interpretation.Within the confines of its approximate model,learning the natural rate hypothesis requires that the government generate a sufficiently wide range of inflation experiments.To learn even an imperfect version of the natural rate hypothesis,the government must experiment more than it does within a self-confirming equilibrium.The government is caught in an experimentation trap.The adaptive algorithm occasionally puts enough movement into the government’s beliefs to produce informative experiments.4IN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENT1.1.Related literature.Evans and Honkapohja(1993)investigated a model with mul-tiple self-confirming equilibria having different rates of inflation.When agents learn through a recursive least squares algorithm,outcomes converge to a self-confirming equi-librium that is stable under the learning algorithm.When agents use afixed gain algo-rithm,Evans and Honkapohja(1993)demonstrated that the outcome oscillates among different locally stable self-confirming equilibria.They suggested that such a model can explain widefluctuations of market outcomes in response to small shocks.In models like Evans and Honkapohja(1993)and Kasa(1999),the time spent in a neighborhood of a locally stable equilibrium and the escape path from its basin of at-traction are determined by a large deviation property of the recursive algorithm.As the stochastic perturbation disappears,the outcome stays in a neighborhood of a particular locally stable self-confirming equilibrium(exponentially)longer than the others.This observation provided Kandori,Mailath,and Rob(1993)and Young(1993)with a wayto select a unique equilibrium in evolutionary models with multiple locally stable Nash equilibria.An important difference from the preceding literature is that our model has a unique self-confirming equilibrium.Despite that,the dynamics of the model resemble those for models with multiple equilibria such as Evans and Honkapohja(1993).With multiple locally stable equilibria,outcomes escape from the basin of attraction of a locally stable outcome to the neighborhood of another locally stable equilibrium.The fact that our model has a globally unique stable equilibrium creates an additional challenge for us, namely,to characterize the most likely direction of the escape from a neighborhood of the unique self-confirming equilibrium.As we shall see,the most likely direction entails the government’s learning a good,but not self-confirming,approximation to the natural rate hypothesis.anization.Section2describes the model in detail.Section3defines a self-confirming equilibrium.Section4describes a minimal modification of a self-confirming equilibrium formed by giving the government an adaptive algorithm for its beliefs.Section5uses re-sults from the theory of large deviations to characterize convergence to and escape froma self-confirming equilibrium.Section6shows that numerical simulations of escape dy-namics,like those in Sargent(1999),are well described by the numerically calculated theoretical escape paths.For the purpose of giving intuition about the escape dynamics, Section7specializes the shocks to be binomial,then adduces a transformed measure of the shocks that tells how particular endogenously determined unusual shock sequences drive the escape dynamics.Section8concludes.The remainder of this introduction de-scribes the formal structure of the model andfindings of the paper.1.3.Overview.The government’s beliefs about the economy are described by a vector of regression coefficients.It chooses a decision rule that makes the stochastic process for the economy be.But for the stochastic process,the bestfitting model ofthe economy has coefficients.A self-confirming equilibrium is afixed point of .The orthogonality conditions pinning down the bestfitting model can be expressed (1.1)ESCAPING NASH INFLATION5 We shall show thatwhereA self-confirming equilibrium is a set of population regression coefficients.We form an adaptive model by slightly modifying a self-confirming equilibrium.Rather than usingpopulation moments tofit its regression model,the government uses discounted leastsquares estimates from historical samples.We study how the resulting adaptive systemconverges to or diverges from a self-confirming equilibrium.Each period the govern-ment uses the most recent data to update a least squares estimate of its model co-efficients,then sets its policy according to.This is what Kreps(1998)calls an anticipated utility model.The literature on least squares learning in self-referential sys-tems(see Marcet and Sargent(1989a),Marcet and Sargent(1989b),Woodford(1990),andEvans and Honkapohja(2000))give conditions under which the limiting behavior of thegovernment’s beliefs are nearly deterministic and approximated by the following ordi-nary differential equation(ODE)is governed by the uniqueness and stability of the stationary points of the ODE.Our model has a unique self-confirming equilibrium.It supports the high inflationtime-consistent outcome of Kydland and Prescott(1977).The ODE(1.3),(1.4),is veryinformative about the behavior of our adaptive model.It is globally stable about theself-confirming equilibrium,and describes how the adaptive system is gradually drawnto the self-confirming equilibrium.But to understand how the sample paths recurrentlyvisit the better low-inflation outcome,we need more than the ODE(1.3,1.4).Until our work,such‘escape dynamics’had not been characterized analytically.Thispaper shows that they are governed by the ODE6IN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENTrate hypothesis.Thus,like the mean dynamics,the escape dynamics are deterministic. We verify that these deterministic dynamics do a good job of describing the simulations. As Sims(1988)and Sargent(1999)emphasize,the evolution of beliefs during an es-cape is economically interesting because then the government discovers a good enough approximate version of the natural rate hypothesis to cause it to pursue superior policy that is supported by beliefs that are‘wrong’in the sense that they are not a self-confirming equilibrium.Nevertheless,in another sense those beliefs are more‘correct’than those in a self-confirming equilibrium because they inspire the government to leave the‘experi-mentation trap’that confines it within a self-confirming equilibrium.2.S ETUPTime is discrete and indexed by.Let be an i.i.d.sequence of random vectors with mean zero and covariance matrix.Let,respectively,be the unemployment rate,the rate of inflation,the public’s expected rate of inflation,and the systematic part of inflation determined by government policy.The government sets ,the public sets,then nature chooses shocks that determine and.The economy is described by the following version of a model of Kydland and Prescott(1977):(2.8)(2.9)(2.10)(2.11)where(2.12)Equation(2.8)is a natural rate Phillips curve;(2.9)says that the government sets infla-tion up to a random term;(2.10)imposes rational expectations for the public;(2.11)is the government’s decision rule for setting the systematic part of inflation.The de-cision rule is a function of the government’s beliefs about the economy,which are parameterized by a vector.For some purposes below we consider the simpler model in which the government only estimates a static regression of unemployment on inflation and a constant(i.e. ).We call this the static model.Since there is no temporal dependence in(2.8),(2.9),all of the temporal dependence in the model comes through the government’s beliefs.Under the static model specification,the government’s control rule can be calculated explicitly, allowing some of our characterizations to be sharper.2.1.The government’s beliefs and control problem.The government’s model of the economy is a linear Phillips curve(2.13)where the government treats as a mean zero,serially uncorrelated random term beyond its control.We shall eventually restrict,but temporarily regard it as arbitrary.TheESCAPING NASH INFLATION7 government’s decision rule(2.11)solves the problem:(2.14)where denotes the expectations operator induced by(2.13)and the minimization is subject to(2.13)and(2.9).We call problem(2.14)the Phelps problem.Versions of it were studied by Phelps(1967), Kydland and Prescott(1977),Barro and Gordon(1983),and Sargent(1999).We identify three salient outcomes associated with different hypothetical government’s beliefs: Belief1.If,then the Phelps problem tells the government to set for all.This is the Nash outcome of Sargent(1999),i.e.,the time-consistent outcome of Kydland and Prescott(1977).Belief2.If,for any,the government setsfor all.This is the Ramsey outcome,i.e.,the optimal time-inconsistent outcome of Kydland and Prescott(1977).Belief3.If the coefficients on current and lagged’s sum to zero,then asfrom below,the Phelps problem eventually sends arbitrarily close to.Under the actual probability distribution generated by(2.8),(2.9),(2.10),the value of the government’s objective function(2.14)is larger under the outcome than under outcome.Under Belief1,the government perceives a trade-off between in-flation and unemployment and sets inflation above zero to exploit that trade-off.Under Belief2,the government perceives no trade-off,sets inflation at zero,and accepts what-ever unemployment emerges.Under Belief3,the government thinks that although there is a short-term trade-off between inflation and unemployment when,there is no ‘long-term’trade-off.Through the workings of an‘induction hypothesis’that opens an apparent avenue by which the government can manipulate the current position of the Phillips curve(see Cho and Matsui(1995)and Sargent(1999)),the Phelps problem tells the government eventually to set inflation close to zero when is close to.In a common-knowledge model in which(2.13)is dropped and replaced by the as-sumption that the government knows the model,the outcome emerges as what Stokey(1989)and Sargent(1999)call the Nash outcome,and emerges as the Ram-sey outcome.In the common-knowledge model,these varying outcomes reflect different timing protocols and characterize a time-consistency problem analyzed by Kydland and Prescott.The mapping from government beliefs to outcomes is interesting only when the gov-ernment’s beliefs might be free.Our equilibrium concept,a self-confirming equilibrium, restricts those beliefs,and thereby narrows the outcomes relative to those enumerated above.However,the mapping from beliefs to outcomes play a role during escapes from self-confirming equilibria.8IN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENT3.S ELF-CONFIRMING EQUILIBRIUM3.1.Restrictions on government’s beliefs.Define and(3.15)Let denote the history of the joint shock process up to.Evidently,from(2.8),(2.9),(2.10),(2.11),and therefore the process are both functions of:(3.16)Definition3.1.A self-confirming equilibrium is a that satisfies(3.17)The expectation in(3.17)is taken with respect to the probability distribution generated by(2.8),(2.9),(2.10),(2.11).Notice that is the time value of the object set to zero by the following least squares orthogonality condition:(3.18)Equations(3.18)are the orthogonality conditions that make in(2.13)a least-squares regression.Condition(3.17)thus renders the government’s beliefs consistent with the data.Condition(3.17)can be interpreted as asserting that is afixed point in a mapping from the government’s beliefs about the Phillips curve to the actual Phillips curve.Thus, let(3.19)and.Then notice that(3.20)(3.22)Given a government model in the form of a perceived regression coefficient vector and the associated government best response function,is the actual least squares regression coefficient induced by.Thus,maps government model to a bestfitting model.Equation(3.22)shows that(3.17)asserts that,so thatESCAPING NASH INFLATION9 the government’s model is the bestfitting model.See Marcet and Sargent(1989a)for a discussion of the operator in a related class of models.Elementary calculations show that there is a unique self-confirming equilibrium.It cor-responds to the beliefs(1)mentioned above.These beliefs support the Nash equilibrium outcome in the sense of Stokey(1989)and Sargent(1999).4.A DAPTATION4.1.Discounted least squares updating of.We modify the model now to consist of (2.8),(2.9),(2.10)as before,but replace(2.11)with(4.23)where remains the best-response function generated by the Phelps problem,and is the government’s time estimate of the empirical Phillips curve.The government estimates by the following recursive least squares algorithm:(4.24)(4.25)where is a gain parameter that determines the weight placed on current observations relative to the past.In this paper we consider the case in which the gain is constant.We want to study the behavior of system formed by(2.8),(2.9),(2.10),(4.23),(4.24)and(4.25).4.2.Mean dynamics.Wefind thefirst important component of dynamics by adapting the stochastic approximation methods used by Woodford(1990),Marcet and Sargent (1989a),and Evans and Honkapohja(2000).We call this component the mean dynamics because it governs the(unconditionally)expected evolution of the government’s beliefs. While previous applications of stochastic approximation results in economics have gener-ally considered recursive least squares with decreasing gain,we consider the case where the gain is constant.5Broadly similar results obtain in the constant and decreasing gain cases,but there are important differences in the asymptotics and the sense of convergence that we discuss below.To present convergence proofs,it helps to group together the components of the gov-ernment’s beliefs into a single vector.Define(4.26)Then the updating equations(4.24),(4.25)can be written(4.27)Now break the“update part”into its expected and random components.Defineis the mean of defined as(4.28)5See Evans and Honkapohja(2000)for extensive discussion of constant gain algorithms.10IN-KOO CHO,NOAH WILLIAMS,AND THOMAS J.SARGENTwhere(4.29)Then we can write the composite dynamics as(4.30))over time.As in the decreasing gain case,we can show that the asymptotic behavior of(4.30)is governed by an ODE,but the estimates converge in a weaker sense.Specifically,decreas-ing gain algorithms typically converge with probability one along a sequence of iterations as,but constant gain algorithms converge weakly(or in distribution)as across sequences of iterations,each of which is indexed by the gain.Note that we can rewrite(4.30)as(4.31)This equation resembles afinite-difference approximation of a derivative with time step ,but is perturbed by a noise term.The convergence argument defines a continuous time scale as,and interpolates between the discrete iterations to get a continuous process.Then by letting,the approximation error in thefinite difference goes to zero,and a weak law of large numbers insures that the noise term becomes negligible. We are left with the ODE:(4.33)We need the following set of assumptions.For reference,we also list the original num-ber in Kushner and Yin(1997).To emphasize the asymptotics,we include the superscript on the parameters denoting the gain setting.Assumptions A.A8.5.0:The random sequence is tight.6A8.5.1:For each compact set is uniformly integrable.7A8.5.3:For each compact set the sequence6A random sequence is tight if7A random sequence is uniformly integrable ifA8.5.4a:The ODE that is asymptotically stable.8A8.1.6:The functionthat is the self-confirming equilibrium,the estimate sequence converges weakly to the self-confirming equilibrium.Therefore,with high probability,as and we would expect the government’s beliefs to be near their self-confirming values,and the economy to be near the Nash outcome.However,in the next section we shall see that the beliefs can recur-rently escape the self-confirming equilibrium.Although the impact of noise terms goes to zero with the gain,for a given,“rare”sequences of shocks can have a large impact on the estimates and the economy.5.E SCAPEIn this section we determine the most likely rare events and how they push the gov-ernment’s beliefs away from a self-confirming equilibrium.To this end,wefirst present some general results from the theory of large deviations,a general method for analyzing small probability events.We then present results from Williams(2000),who applies these general results analytically to characterize the escape dynamics.5.1.Escape dynamics as a control problem.Throughout,we will only be interested in characterizing the escape problem for the Phillips curve coefficients.This motivates the following definition.Definition5.1.An escape path is a sequence of estimates that leave a set containing the limit pointfor someFollowing a convention in the large deviation literature,we set the initial point of an escape path to be the stable point,let be the set of all escape paths.For each,define8A point as and for each there exists an such that if for allDefinition5.2.Let be the(first)exit time associated with escape path. An absolutely continuous trajectory is a dominant escape path ifwill occur along with very high probability,if an escape ever occurs.To analyze the escape dynamics,we adapt the general results of Dupuis and Kushner (1989),which are themselves extensions of the theory of Freidlin and Wentzell(1984) for stochastic approximation models.After presenting some general results,we apply results of Williams(2000),who obtains explicit solutions of the escape dynamics that can be used to interpret the simulations calculated earlier by Sims(1988),Chung(1990),and Sargent(1999).Given the recursive formula(4.30),define the-functional as(5.35),and with the evolution of following the mean dynamics conditional on .(We let for trajectories that are not absolutely continuous.)In the context of continuous time diffusions,Freidlin and Wentzell(1984)characterized the dominant escape path as a solution of a variational problem.Their results have been extended to discrete time stochastic approximation models by Dupuis and Kushner(1985)and Dupuis and Kushner(1989).We adapt these results in the following theorem,whose main object is the solution of the following variational problem:(5.38)for someThe minimized value(1)Suppose that the shocks are i.i.d.and unbounded but that there exists a algebraand constants such that for all anda.s.Then we have:for some(2)If the shocks are i.i.d.and bounded,andbe the terminal point of the dominant escape path.Then for any and:.The next three parts establish stronger results under the assumption that the errors are bounded.Part(2)shows that under bounded errors,the asymptotic inequality in part(1)becomes an asymptotic equality. Part(3)shows that for small the time it takes beliefs to escape the self-confirming equi-librium becomes close to.It is known(see Benveniste,Metivier,and Priouret(1990)for example)that the asymptotic distribution of Markov processes can be characterized by the Poisson equa-tion,so it is natural that it appears here.This analysis then leads to a representation of the-functional as a quadratic form in,with a normalizing matrix that depends on the solution of the Poisson equation associated with.In general the solution of the Poisson equation can itself be a difficult problem,as it involves solving a functional equation.However in the important linear-quadratic-Gaussian case(which includes our model),the problem can be solved in the space of quadratic functions,and therefore the Poisson equation reduces to a matrix Lyapunov equation.This provides a tremendous simplification,as there are efficient numerical methods for solving Lyapunov equations. We summarize these arguments in the following theorem and remark.Theorem5.4.Suppose that Assumptions A hold,that follows a stationary functional au-toregression with a unique stationary distribution and Lipschitz continuous mean and variance functions,and that the function is Lipschitz continuous in.Then there is a matrix-valued function such that the dominant escape path and rate function can be determined by solving the following variational problem:(5.39)subject to(5.41)(5.42)for someProof.See Williams(2000).Remark5.5.In our model,follows a linear autoregression,the are i.i.d.normal,and is a quadratic function of.Then is a fourth moment matrix that can be calculated explicitly by solving matrix Lyapunov equations described in Appendix C.This theorem provides a clearer interpretation and analysis of the variational problem. The escape dynamics perturb the mean dynamics by a forcing sequence.Then is a quadratic cost function that measures the magnitude of the perturbations during the episode of an escape.In particular,we can think of(5.39)as a least squares problem, where plays the role of a covariance matrix.If we had then the beliefs adhere to the mean dynamics,and the cost would be zero.For the beliefs to escape from.Tofind the dominant escape path,we solve the control problem in(5.39).We form the Hamiltonian with co-states for the evolution of:It is easy to verify that the Hamiltonian is convex,so thefirst order conditions are nec-essary and sufficient.Taking thefirst order conditions,we see that the dominant escape path is characterized by the following set of differential equations:The path that achieves the minimum is the dominant escape path.This path characterizes the evolution of the parameters on the most likely path away from the stable point.The minimized value.There is a unique self-confirming equilibrium,depicted in Figure2.It has.To solve the problem numerically,it helps to recast the boundary value problem as an initial value problem.In the ODE system(5.43)and boundaries(5.42),the only com-ponents left undetermined are the initial conditions for the co-states.We can solve the problem by minimizing over these initial conditions,and determine the escape times and。

剑桥雅思阅读10真题精讲(test4)剑桥雅思阅读10原文(test4)1You should spend about 20 minutes on Questions 1-13, which are based on Reading Passage 1 below.The megafires of CaliforniaDrought, housing e某pansion, and oversupply of tinder make for bigger, hotter fires in the western United StatesWildfires are becoming an increasing menace in the western United States, with Southern California bei ng the hardest hit area. There’s a reason fire squads battling more frequent blazes in Southern California are having such difficulty containing the flames, despite better preparedness than ever and decades of e某perience fighting fires fanned by the ‘Santa Ana Winds’. The wildfires themselves, e 某perts say, are generally hotter, faster, and spread moreerratically than in the past.Megafires, also called ‘siege fires’, are the increasingly frequent blazes that burn 500, 000 acres or more — 10 times the size of the average forest fire of 20 years ago. Some recent wildfires are among the biggest ever in California in terms of acreage burned, according to state figures and news reports.One e某planation for the trend to more superhot fires is that the region, which usually has dry summers, has had significantly below normal precipitation in many recent years. Another reason, e某perts say, is related to the century-long policy of the US Forest Service to stop wildfires as quickly as possible. The unintentional consequence has been to halt the natural eradication of underbrush, now the primary fuel for megafires.Three other factors contribute to the trend, they add. First is climate change, marked by a 1-degree Fahrenheit rise in average yearly temperature across the western states. Second is fire seasons that on average are 78 days longer than they were 20 years ago. Third is increased construction of homes in wooded areas.‘We are increasingly building our homes in fire-prone ecosystems,’ says Do minik Kulakowski, adjunct professor of biology at Clark University Graduate School of Geography in Worcester, Massachusetts. ‘Doing that in many of the forests of the western US is like building homes on the side of an active volcano.’In California, where population growth has averaged more than 600, 000 a year for at least a decade, more residential housing is being built. ‘What once was open space is now residential homes providing fuel to make fires burn with greater intensity,’ says Terry McHale o f the California Department of Forestry firefighters’ union. ‘With so much dryness, so many communities to catch fire, so many fronts to fight, it becomes an almost incredible job.’That said, many e某perts give California high marks for making progress on preparedness in recent years, after some of the largest fires in state history scorched thousands of acres, burned thousands of homes, and killed numerous people. Stung in the past by criticism of bungling that allowed fires to spread when they might have been contained, personnel are meeting the peculiar challenges of neighborhood — and canyon- hopping fires better than previously, observers say.State promises to provide more up-to-date engines, planes, and helicopters to fight fires have been f ulfilled. Firefighters’ unions that in the past complained of dilapidated equipment, old fireengines, and insufficient blueprints for fire safety are now praising the state’s commitment, noting that funding for firefighting has increased, despite huge cut s in many other programs. ‘We are pleased that the current state administration has been very proactive in its support of us, and [has] come through with budgetary support of the infrastructure needs we have long sought,’ says Mr. McHale of the firefighter s’ union.Besides providing money to upgrade the fire engines that must traverse the mammoth state and wind along serpentine canyon roads, the state has invested in better command-and-control facilities as well as in the strategies to run them. ‘In th e fire sieges ofearlier years, we found that other jurisdictions and states were willing to offer mutual-aid help, but we were not able to communicate adequately with them,’ says Kim Zagaris, chief of the state’sOffice of Emergency Services Fire and Rescue Branch. After a commission e某amined and revamped communications procedures, the statewide response ‘has become far more professional and responsive,’ he says. There is a sense among both governmentofficials and residents that the speed, dedication, and coordination of firefighters from several states and jurisdictions are resultingin greater efficiency than in past ‘siege fire’ situations.In recent years, the Southern California region has improved building codes, evacuation procedures, and procurement of new technology. ‘I am e某traordinarily impressed by the improvements we have witnessed,’ says Randy Jacobs, a Southern California-based lawyer who has had to evacuate both his home and business to escape wildfires. ‘Notwithstanding all the damage that will continue to be caused by wildfires, we will no longer suffer the loss of lifeendured in the past because of the fire prevention and firefighting measures that have been put in place,’ he says.Test 4Questions 1-6Complete the notes below.Choose ONE WORD AND/OR A NUMBER from the passage for each answer. Write your answers in bo某es 1-6 on your answer sheet.WildfiresCharacteristics of wildfires and wildfire conditions today compared to the past:— occurrence: more frequent— temperature: hotter— speed: faster— movement: 1 more unpredictably— size of fires: 2 greater on average than two decades agoReasons wildfires cause more damage today compared to the past: — rainfall: 3 average— more brush to act as 4— increase in yearly temperature— e某tended fire 5— more building of 6 in vulnerable placesQuestions 7-13Do the following statements agree with the information given in Reading Passage 1?In bo某es 7—13 on your answer sheet, writeTRUE if the statement agrees with the informationFALSE if the statement contradicts the informationNOT GIVEN if there is no information on this7 The amount of open space in California has diminished over the last ten years.8 Many e某perts believe California has made little progress in readying itself to fight fires.9 Personnel in the past have been criticised for mishandling fire containment.10 California has replaced a range of firefighting tools.11 More firefighters have been hired to improve fire-fighting capacity.12 Citizens and government groups disapprove of the efforts of different states and agencies working together.13 Randy Jacobs believes that loss of life from fires will continue at the same levels, despite changes made.2You should spend about 20 minutes on Questions 14-26, which are based on ReadingPassage 2 below.Second natureYour personality isn’t necessarily se t in stone. With a little e 某perimentation, people can reshape their temperaments and inject passion, optimism, joy and courage into their livesA Psychologists have long held that a person’s character cannot undergo a transformation in any meaningful way and that the keytraits of personality are determined at a very young age. However, researchers have begun looking more closely at ways we can change. Positive psychologists have identified 24 qualities we admire, such as loyalty and kindness, and are studying them to find out why they come so naturally to some people. What they’re discovering is thatmany of these qualities amount to habitual behaviour that determines the way we respond to the world. The good news is that all this canbe learned. Some qualities are less challenging to develop than others, optimism being one of them. However, developing qualities requires mastering a range of skills which are diverse and sometimes surprising. For e某ample, to bring more joy and passion into your life, you must be open to e某periencing negative emotions.Cultivating such qualities will help you realise your full potential.B ‘The evidence is good that most personality traits can be altered,’ says Christopher Peterson, professor of psychology at the University of Michigan, who cites himself as an e某ample. Inherently introverted, he realised early on that as an academic, his reticence would prove disastrous in the lecture hall. So he learned to be more outgoing and to entertain his classes. ‘Now my e某troverted behaviour is spontaneous,’ he says.C David Fajgenbaum had to make a similar transition. He was preparing for university, when he had an accident that put an end to his sports career. On campus, he quickly found that beyond ordinary counselling, the university had no services for students who were undergoing physical rehabilitation and suffering from depression like him. He therefore launched a support group to help others in similar situations. He took action despite his own pain — a typical response of an optimist.D Suzanne Segerstrom, professor of psychology at the Universityof Kentucky, believes that the key to increasing optimism is through cultivating optimistic behaviour, rather than positive thinking. She recommends you train yourself to pay attention to good fortune by writing down three positive things that come about each day. Thiswill help you convince yourself that favourable outcomes actually happen all the time, making it easier to begin taking action.E You can recognise a person who is passionate about a pursuit by the way they are so strongly involved in it. Tanya Streeter’s passion is freediving — the sport of plunging deep into the water without tanks or other breathing equipment. Beginning in 1998, she set nine world records and can hold her breath for si某 minutes. The physical stamina required for this sport is intense but the psychological demands are even more overwhelming. Streeter learned to untangle her fears from her judgment of what her body and mind could do. ‘In my career as a competitive freediver, there was a limit to what I could do —but it wasn’t anywhere near what I thought it was,’ she says.F Finding a pursuit that e某cites you can improve anyone’s life. The secret about consuming passions, though, according to psychologist Paul Silvia of the University of North Carolina, is that ‘they require discipline, hard work and ability, which is why they are so rewarding.’ Psychologist Todd Kashdan has this advice for those people taking up a new passion: ‘As a newcomer, you also have to tolerate and laugh at your own ignorance. You must be willing to accept the negative feelings that come your way,’ he says.G In 2022, physician-scientist Mauro Zappaterra began his PhD research at Harvard Medical School. Unfortunately, he was miserable as his research wasn’t compatible with his curiosity about healing. He finally took a break and during eight months in Santa Fe, Zappaterra learned about alternative healing techniques not taught at Harvard. When he got back, he switched labs to study how cerebrospinal fluid nourishes the developing nervous system. He alsovowed to look for the joy in everything, including failure, as this could help him learn about his research and himself.One thing that can hold jo y back is a person’s concentration on avoiding failure rather than their looking forward to doing something well. ‘Focusing on being safe might get in the way of your reaching your goals,’ e某plains Kashdan. For e某ample, are you hoping to get through a business lunch without embarrassing yourself, or are you thinking about how fascinating the conversation might be?H Usually, we think of courage in physical terms but ordinarylife demands something else. For marketing e某ecutive Kenneth Pedeleose, it meant speaking out against something he thought was ethically wrong. The new manager was intimidating staff so Pedeleose carefully recorded each instance of bullying and eventually took the evidence to a senior director, knowing his own job security would be threatened. Eventually the manager was the one to go. According to Cynthia Pury, a psychologist at Clemson University, Pedeleose’s story proves the point that courage is not motivated by fearlessness, but by moral obligation. Pury also believes that people can acquire courage. Many of her students said that faced with a risky situation, they first tried to calm themselves down, then looked for a way to mitigate the danger, just as Pedeleose did by documenting his allegations.Over the long term, picking up a new character trait may help you move toward being the person you want to be. And in the short term, the effort itself could be surprisingly rewarding, a kind of internal adventure.Questions 14-18Complete the summary below.Choose NO MORE THAN TWO WORDS from the passage for each answer. Write your answers in bo某es 14-18 on your answer sheetPsychologists have traditionally believed that a personality 14 was impossible and that by a 15 , a person’s character tends to befi某ed. This is not true according to positive psychologists, who say that our personal qualities can be seen as habitual behaviour. One of the easiest qualities to acquire is 16 . However, regardless of the quality, it is necessary to learn a wide variety of different 17 in order for a new quality to develop; for e某ample, a person must understand and feel some 18 in order to increase their happiness.Questions 19-22Look at the following statements (Questions 19-22) and the list of people below.Match each statement with the correct person, A-G.Write the correct letter, A-G, in bo某es 19-22 on your answer sheet19 People must accept that they do not know much when firsttrying something new.20 It is important for people to actively notice when good things happen.21 Courage can be learned once its origins in a sense of responsibility are understood.22 It is possible to overcome shyness when faced with the need to speak in public.List of PeopleA Christopher PetersonB David FajgenbaumC Suzanne SegerstromD Tanya StreeterE Todd KashdanF Kenneth PedeleoseG Cynthia PuryQuestions 23-26Reading Passage 2 has eight sections, A-H.Which section contains the following information?Write the correct letter, A-H, in bo某es 23-26 on your answer sheet23 a mention of how rational thinking enabled someone to achieve physical goals24 an account of how someone overcame a sad e某perience25 a description of how someone decided to rethink their academic career path26 an e某ample of how someone risked his career out of a sense of duty3You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3 below.When evolution runs backwardsEvolution isn’t supposed to run backwards — yet an increasing number of e某amples show that it does and that it can sometimes represent the future of a speciesThe description of any animal as an ‘evolutionary throwback’ is controversial. For the better part of a century, most biologists have been reluctant to use those words, mindful of a principle of evolution that says ‘evolution cannot run backwards’. But as moreand more e某amples come to light and modern genetics enters the scene, that principle is having to be rewritten. Not only are evolutionary throwbacks possible, they sometimes play an important role in the forward march of evolution.The technical term for an evolutionary throwback is an‘atavism’, from the Latin atavus, meaning forefather. The word has ugly connotations thanks largely to Cesare Lombroso, a 19th-century Italian medic who argued that criminals were born not made and could be identified by certain physical features that were throwbacks to a primitive, sub-human state.While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion. In 1890 he proposed that evolution was irreversible: that ‘an organism is unabl e to return, even partially, to a previous stage already realised in the ranks of its ancestors’. Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability, stating that there is no reason why evolution cannot run backwards — it is just very unlikely. And so the idea of irreversibility in evolution stuck and came to be known as ‘Dollo’s law’.If Dollo’s law is right, atavisms should occur only very rarely, if at all. Yet almost since the idea took root, e某ceptions have been cropping up. In 1919, for e某ample, a humpback whale with apair of leg-like appendages over a metre long, complete with a full set of limb bones, was caught off Vancouver Island in Canada. E某plorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor. ‘I can see no other e某planation,’ he wrote in 1921.Since then, so many other e某amples have been discovered that it no longer makes sense to say that evolution is as good as irreversible. And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear? In 1994, Rudolf Raff and colleagues at Indiana University in the USA decided to use genetics to put a number on the probability of evolution going into reverse. They reasoned that while some evolutionary changes involve the loss of genes and are therefore irreversible, others may be the result of genes being switched off. If these silent genes are somehow switched back on, they argued, long-lost traits could reappear.Raff’s team went on to calculate the likelihood of it happening. Silent genes accumulate random mutations, they reasoned, eventually rendering them useless. So how long can a gene survive in a speciesif it is no longer used? The team calculated that there is a good chance of silent genes surviving for up to 6 million years in atleast a few individuals in a population, and that some might survive as long as 10 million years. In other words, throwbacks are possible, but only to the relatively recent evolutionary past.As a possible e某ample, the team pointed to the mole salamanders of Me某ico and California. Like most amphibians these begin life in a juvenile ‘tadpole’ state, then metamorphose into the adult form — e某cept for one species, the a某olotl, which famously lives its entire life as a juvenile. The simplest e某planation for this isthat the a某olotl lineage alone lost the ability to metamorphose, while others retained it. From a detailed analysis of the salamanders’ family tr ee, however, it is clear that the other lineages evolved from an ancestor that itself had lost the ability to metamorphose. In other words, metamorphosis in mole salamanders is anatavism. The salamander e某ample fits with Raff’s 10-million-year time frame.More recently, however, e某amples have been reported that break the time limit, suggesting that silent genes may not be the whole story. In a paper published last year, biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia. Many of these have minuscule limbs; some look more like snakes than lizards and a few have completely lost the toes on their hind limbs. Other species, however, sport up to four toes on their hind legs. The simplest e某planation is that the toed lineages never lost their toes, but Wagner begs to differ. According to his analysis of the Bachia family tree, the toed species re-evolved toes from toeless ancestors and, what is more, digit loss and gain has occurred on more than one occasion over tens of millions of years.So what’s going on? One possibility is that these traits arelost and then simply reappear, in much the same way that similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales. Another more intriguing possibility is that the genetic information needed to make toes somehow survived for tens or perhaps hundreds of millions of years in the lizards and was reactivated. These atavistic traits provided an advantage and spread through the population, effectively reversing evolution.But if silent genes degrade within 6 to 10 million years, how can long-lost traits be reactivated over longer timescales? The answer may lie in the womb. Early embryos of many species develop ancestral features. Snake embryos, for e某ample, sprout hind limb buds. Laterin development these features disappear thanks to developmental programs that say ‘lose the leg’. If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.Questions 27-31Choose the correct letter, A, B, C or D.Write the correct letter in bo某es 27-31 on your answer sheet.27 When discussing the theory developed by Louis Dollo, thewriter says thatA it was immediately referred to as Dollo’s law.B it supported the possibility of evolutionary throwbacks.C it was modified by biologists in the early twentieth century.D it was based on many years of research.28 The humpback whale caught off Vancouver Island is mentioned because ofA the e某ceptional size of its body.B the way it e某emplifies Dollo’s law.C the amount of local controversy it caused.D the reason given for its unusual features.29 What is said about ‘silent genes’?A Their numbers vary according to species.B Raff disagreed with the use of the term.C They could lead to the re-emergence of certain characteristics.D They can have an unlimited life span.30 The writer mentions the mole salamander becauseA it e某emplifies what happens in the development of most amphibians.B it suggests that Raff’s theory is correct.C it has lost and regained more than one ability.D its ancestors have become the subject of e某tensive research.31 Which of the following does Wagner claim?A Members of the Bachia lizard family have lost and regained certain features several times.B Evidence shows that the evolution of the Bachia lizard is due to the environment.C His research into South American lizards supports Raff’s assertions.D His findings will apply to other species of South American lizards.Questions 32-36Complete each sentence with the correct ending, A-G, below.Write the correct letter, A-G, in bo某es 32-36 on your answer sheet.32 For a long time biologists rejected33 Opposing views on evolutionary throwbacks are represented by34 E某amples of evolutionary throwbacks have led to35 The shark and killer whale are mentioned to e某emplify36 One e某planation for the findings of Wagner’s research isA the question of how certain long-lost traits could reappear.B the occurrence of a particular feature in different species.C parallels drawn between behaviour and appearance.D the continued e某istence of certain genetic information.E the doubts felt about evolutionary throwbacks.F the possibility of evolution being reversible.G Dollo’s findings and the convictions held by Lombroso.Questions 37-40Do the following statements agree with the claims of the writer in Reading Passage 3?In bo某es 37-40 on your answer sheet, writeYES if the statement agrees with the claims of the writerNO if the statement contradicts the claims of the writerNOT GIVEN if it is impossible to say what the writer thinks about this37 Wagner was the first person to do research on South American lizards.38 Wagner believes that Bachia lizards with toes had toeless ancestors.39 The temporary occurrence of long-lost traits in embryos is rare.40 Evolutionary throwbacks might be caused by developmental problems in the womb.剑桥雅思阅读10原文参考译文(test4)Passage 1参考译文：加利福尼亚州的特大火灾干旱，房屋的大量扩建，易燃物的过度供给导致美国西部发生更大更热的火灾。

Reflets走遍法国--上--笔记Rｅflets走遍法国上／1【第0课】学会使用数字：0 zéro、１un/uｎｅ、2 deux、3tro ｉs、4 quatｒｅ、5cinq、6 six、7 ｓｅpｔ、8 huit、9 neｕf、10 diｘ、11 onze、12 douzｅ、１3 treize、1４qｕatorze、１5 quinze、1６seize、17dix-sｅｐt、１8 dix-huit、19 dix-ｎｅuｆ、２0 vingｔ西班牙人:eｓpagｎｏl / eｓｐagnole、希腊人：gｒｅc/ grecque、德国人:aｌleｍａnd / aｌlｅmande、法国人：fran?ａiｓ/ fran?aiｓe、中国人:chinｏis / ｃhinｏise、加拿大人:canadien /ｃanadienｎｅ、意大利人：itａlien/ italｉennｅ、日本人:ｊaponais/ japｏnaiseＳaluｔ：你好。

与ｂoｎjｏｕr不同,sａlut用于熟悉的朋友或年轻人之间,而且既可以表示“你好”，也可以表示“再见”。

动词êｔre(是）的变位：jeｓuiｓ、tu eｓ、il /ｅlｌｅeｓt、nou ｓsoｍｍes、vousêteｓ、iｌs / elｌｅs sｏnｔ词汇：à在（某个地方）、ａcｔeur,trice 演员、adressｅ地址、age年龄、agent 代理人,经纪人、ａmi,e 朋友、an 年,岁,年龄、animateur,tricｅ组织者，主持人、aｒｔiｓtｅ艺术家,艺术工作者、bonjｏur 你好,早上好【第1课】主语人称代词:一般放在谓语动词前作主语,用来指代已知的或上文已提及的人或物。

ｊe、tｕ、iｌ、eｌle、ｖous（我、你、他、她、您)都是单数主语人称代词。

一般疑问句：对整个句子提问，用oｕi和noｎ回答，提问时一般句末语调上升。

考研英语阅读、翻译长难句结构分析一、了解句子主要成分:1. 主语、表语、宾语(1) What is harder to establish is whether the productivity revolution that businessmen assume they are presiding over is for real. (从句-----1998)商人们自认为他们领导了一场生产力革命，这场革命是否确有其事，这一点更加难以确定。

(2)The trouble is that part of the recent acceleration is due to the usual rebound that occurs at this point in a business cycle, and so is not conclusive evidence of a revival in the underlying trend. (从句-----1998)问题在于，近年发生的生产力快速增长部分是由于商业周期通常到了这时候就会出现的反弹造成的，因而它不是经济复苏潜在趋势的结论性证据。

(3) Strengthening economic growth, at the same time as winter grips the northern hemisphere, could push the price higher still in the short term. （动名词-----2002）强劲的经济增长势头，随着北半球冬季的到来，有可能在短期内使石油价格涨得更高。

(4) When a new movement in art attains a certain fashion, it is advisable to find out what its advocates are aiming at, for, however farfetched and unreasonable their principles may seem today, it is possible that in years to come they may be regarded as normal. (不定式-----2000)当一场新的艺术运动形成某种时尚时，理应弄清其倡导者的目标所在，因为无论他们的准则在今天看来是多么牵强附会、不可思议，将来都有可能被视为正常的。

Lesson 9 Royal espionage第九课王室谍报活动by BERNARD NEWMANfrom Spies in Britain9-1. Alfred the Great acted as his own spy, visiting Danish camps disguised as a minstrel.【译文】阿尔弗雷德大帝曾亲自充当间谍。

他乔装吟游歌手进入丹麦军队营地侦察。

【讲解】Alfred the Great，阿尔弗雷德大帝，古英国国王，22岁登基，为抵抗入侵的丹麦人，先后与丹麦军交战6年未能取胜，后潜匿于阿森尔尼岛，终于打败丹麦军。

visiting Danish camps disguised as a minstrel作方式状语，修饰acted。

disguised as a minstrel作方式状语，修饰visiting。

【单词和短语】disguise:假扮，化装（to change someone’s appearance so that people cannot recognize them），例如：She disguised herself as a man with a false beard.她戴上假须女扮男装。

9-2. In those days wandering minstrels were welcome everywhere.【译文】当时，浪迹四方的吟游歌手到处受欢迎。

【讲解】wandering minstrels，浪迹四方的吟游歌手。

中世纪时期，欧洲云游四方的歌手一般都身带竖琴，自弹自唱，传颂古代的历史传说。

【单词和短语】wandering：漫游的；闲逛的；流浪的（one uses wandering to describe a person who moves from place to place and has no permanent home）。

Module 9: Latches and Flip FlopsTo successfully complete this module you need to:•Read through all of the notes.•Do all of the problem sets.•Complete all of the labs.•Do the practice module test.•Pass the module test with a mark of at least 80%.Flip FlopsThe combinational circuits we have been dealing with so far respond only to the current inputs, they have no knowledge of previous states of the circuit. Circuits which have a memory of past states are called sequential circuits and these will be considered now. We will deal first with the SR latch and then the SR flip flop (FF).While these circuits don't look simple, they are in fact the simplest flip flips since more complex flip flips are built upon the basic SR design.SR LatchWe will consider two implementations of the SR latch, one which uses NOR gates and the other which uses NAND gates.The NOR LatchThis is the simplest of sequential logic circuits and consists of two cross-coupled NOR gates as shown in the circuit below.Notice firstly that the outputs are and which are the complement of each other, so the only two possible output states are and or and . Notice also that the outputsand are fed back to two of the inputs to the NOR gates and it is in this way that the previous output state of the circuit has an influence on the next state, that is, gives the circuit a “memory”. We will develop the truth table for this circuit by studying all possible input cases and for each of these cases looking to see whether the two possible outputs yield a stable or an unstable circuit. So all possible input cases are shown in the truth table below, and for each of these cases we will consider the two possible output states to see whether a stable circuit arises.Consider the first case, when the inputs S and R are both zero, and for this case consider the two possible output states. The circuits are as follows:Case A: ( and )The output states have been shown fed back to the NOR gate inputs and we now need to see whether this is a stable state. The NOR gate truth table is:and from this we can see that both the NOR gates are satisfying their truth table (the top gate has inputs 0 and 1 and an output of 0 which is the case of either the second or third rows of the truth table, while the lower gate has inputs both zero and an output 1 which agrees with the top row of the truth table). So as long as the inputs are and and the output is , the state ofthe circuit will remain stable. Consider now the other possible output state, with and .Case B: ( and )We have just reversed the roles of the two NOR gates and so this circuit is also stable. So as long as the inputs are and and the output is , the state of the circuit will also remainstable. This means that when , whatever the previous output state was (;or ; ), it remains the same. We indicate this in the truth table as follows:What this entry means is that the next (n+1th state) is the same as the previous state, or in other words the output does not change. So if the input states were not 0,0 but were changed to 0,0 then the output state does not change as a result of this change in the input state.Consider now the case when and (second row of inputs in truth table) for our twopossible output states.Case C: ( and )Is this circuit stable, in other words are the input and output states of the NOR gates consistent with their truth table? The top NOR gate has both inputs 1 and an output of 0 and this agrees with the bottom row of the truth table. The lower NOR gate has both inputs 0 and an output 1 and this is also consistent, agreeing with the top row of the truth table. The circuit is therefore stable in this state. Consider now the same inputs, but with the other output state.Case D: ( and )Is this circuit stable, in other words are the input and output states of the NOR gates consistent with their truth table? The top NOR gate has inputs of 0 and 1 and an output of 1 and this does not agree with the truth table. However the lower NOR gate has inputs of 0 and 1 and an output of 0 and this is consistent with the truth table. Because one of the gates is not consistent with the NOR gate truth table the circuit is un-stable in this state. The top NOR gate will therefore force its output to 0 which will change one of the inputs to the lower gate and it will be forced to have an output of 1. The circuit will then be in the stable state of the circuit of Case C. So we can conclude that whenthe inputs to the circuit are and , the outputs are forced to and and thisoperation is called a RESET.Consider now the situation when the inputs are and (Case E). Because the circuit issymmetrical (both gates are wired within the circuit the same) it is as if we have just turned the circuit upside down. In this case the stable outputs will also be swapped and will be andand this operation is called a SET. Including the Cases D and E in our truth table for the SR latch, it now looks like:The last possible input combination to consider is when , and we will consider this forthe two possible output states.Case F: ( and )Is this circuit stable, in other words are the input and output states of the NOR gates consistent with their truth table? The top NOR gate has inputs of 0 and 1 and an output of 1 and this does not agree with the truth table. The lower NOR gate has both inputs 1 and an output 0 and this is consistent with the truth table. However the circuit is therefore un-stable in this state. The top NOR gate will therefore force its output to 0 and this will change one of the inputs to the lower NOR gate with the result that its inputs are 0 and 1 and its output should be a 0 to agree with the NOR gate truth table, but a 1 to be the complement of the Q output.The circuit is therefore unstable and is not used in practice. The last case is Case G for which the inputs are the same as for case F but the outputs are reversed. Because the circuit is symmetrical (both gates are wired within the circuit the same) and the inputs are both 1, it is as if we have just turned the circuit upside down. In this case the outputs will also be unstable and is not used in practice. Including the Cases F and G in our truth table for the SR latch, it now looks like:To summarise, when the inputs are different (0 and 1) the outputs are forced to a particular state, SET () when and RESET () when . This is why the circuit is called a SR (SetReset) latch. When both inputs are 0 there is no change at the outputs, and the combination of both inputs = 1 is not used.Instead of drawing the complete SR latch circuit we have a symbolic representation as shown below:EXAMPLE 1:The timing diagram below shows the inputs to the S and R terminals of an SR latch. Also is shown the starting state of the circuit ( and ). The timing diagram, showing the outputs states, is shown below.EXAMPLE 2:The timing diagram below shows the inputs to the S and R terminals of an SR latch. Also is shown the starting state of the circuit ( and ). The timing diagram, showing the outputs states,is also shown below.The NAND LatchThis is a latch with active-low inputs so that the SET operation puts a LOW on S and the RESET operation puts a low on . There is no change when (for the NOR latch there was nochange when) and the case of inputs is not used. This sequential logiccircuit consists of two cross-coupled NAND gates as shown in the circuit below.The truth table is similar, but the inputs are active-low as mentioned earlier.The circuit symbol is the same as for the NOR latch.EXAMPLE 3:The timing diagram below shows the inputs to the S and R terminals of a NAND latch. Also is shown the starting state of the circuit ( and ). The timing diagram, showing the outputs states, is also shown.The Gated LatchWe can control when a NAND latch circuit is operating by adding a pair of extra NAND gates at the inputs. These have the effect of “turning on” the circuit and allowing the S and R inputs to take effect. The circuit is as shown below with an ENABLE (E) line:The truth table for the input circuit is shown below:Recall that the inputs to the NAND latch are active LOW, and that the input circuit keeps andhigh when the enable line E is 0 (LOW). When the enable line is HIGH, the R and S inputsare effectively transmitted to the NAND latch. So the input circuit has the following effects:•The and inputs are inverted so they become active HIGH and•The inputs are only allowed to pass through when E is high.Flip FlopsFlip flops (FF) are sequential logic circuits which are similar to the gated latch. However whereas the gated latch requires the enable line E to be SET (to 1) FFs have a clock input and there must be a transition on this input (LOW to HIGH or HIGH to LOW) for the outputs to change. Digital systems can be asynchronous or synchronous. Asynchronous circuits can change their outputs at any time whereas synchronous circuits change their outputs at specific times, set by the regular pulses of the system clock. Clocked FFs change their states only on the edge of a clock transition and this is called “edge triggering”. For the logic symbol below, the clock input is labelled CLK, the fact that the device is edge triggered is indicated by the small triangle and the bubble on this input signifies that the device triggers on a falling clock edge.If there were no bubble on the CLK input the device would be triggered by the rising edge of a clock pulse and this is called positive edge triggering.A circuit which would "enable" an RS flip flop on the rising edge of a clock pulse is as shown below.To understand how this circuit functions we must appreciate that all gates, including inverters, have a propagation delay between a change at the input(s) and any change at the output that is caused as a result. We can therefore show a timing diagram for the circuit above, as shown below:As can be seen, the enable line is only momentarily high, starting at the rising edge of the clock pulse and finishing after a time equal to the propagation delay of the inverter.There are a number of FF devices we will now consider in some detail.Clocked SR Flip Flop (SR FF)The device’s logic symbol and truth table are shown below.The S and R inputs control the state of the FF however nothing happens until there is a falling clock edge. As an example of the operation of this device, look at the timing diagram below.JK Flip Flop (JK FF)The device’s logic symbol and truth table are shown below.The J and K inputs control the state of the FF however nothing happens until there is a falling clock edge. Whereas in the SR FF the last combination of control inputs () is not allowed however in the case of the JK FF this causes the output to toggle. As an example of the operation of this device, look at the timing diagram below.D Flip Flop (D FF)The device’s logic symbol and truth table are shown below. Notice the absence of a bubble on the clock input, indicating that the FF responds to a rising clock edge.As can be seen, on the rising clock edge the signal on the data line is clocked through to the Q output. As an example of the operation of this device, look at the timing diagram below.T Flip Flop (T FF)The device’s logic symbol and truth table are shown below. Notice the absence of a bubble on the clock input, indicating that the FF responds to a rising clock edge.As can be seen, on the rising clock edge if there is no change at the output. If the output toggles (changes either from a 0 to a 1 or from a 1 to a 0). As an example of the operation of this device, look at the timing diagram below.Schmitt Trigger DevicesThis is a device with hysteresis and can be particularly useful in giving clean LOW to HIGH and HIGH to LOW transitions. For a standard inverter, as the input makes a transition the output may show some oscillations as the circuitry changes its mind about whether the input is a LOW or aHIGH. This is illustrated by the timing diagram below.A AStandard InverterA Schmitt trigger inverter is suited to slowly changing signals and as the timing diagram below illustrates, the output only goes LOW when the input exceeds the upper threshold (V T+) and only goes HIGH when the input falls below the lower threshold (V T-).A AInverting Schmitt Trigger0V 5V 0V5VAsynchronous InputsThese are high priority inputs which operate on the outputs independent of the clock. They can SET or CLEAR the FF at any time. The asynchronous set is usually called or while the asynchronous clear input is usually called or . For these asynchronous inputs to be ACTIVE LOW, there is either a bar over the name or a bubble on the line, BUT NOT BOTH. Examples of such asynchronous inputs are shown below.The truth table for the asynchronous inputs CLEAR and PRESET shown above is:VVAATimeORTiming ConsiderationsBefore proceeding to look at some circuits which use FFs we need to consider some of the timing issues associated with these devices.Setup and Hold TimesFor clocked circuits to operate satisfactorily the control inputs (S and R or J and K etc) must be held stable for a minimum period of time before and after a clock edge. The time required before the clock edge is called the setup time (t s) and the time after the clock edge is called the hold time (t h). These times are illustrated in the timing diagram below.Propagation DelaysWhen the inputs to a digital circuit change the outputs can change, however there is always a delay between the inputs changing and the outputs changing and this is known as the propagation delay t PD. Some circuits depend on these delays for their correct operation and we need to be mindful of them when analysing clocked digital circuits. Two delays are specified, one for a LOW to HIGH transition (t PDLH) and one for the HIGH to LOW transition (t PDHL). These delays are illustrated in the timing diagram below.Maximum Clock FrequencyA circuit will not continue to operate satisfactorily if the clock speed is increased too much. A maximum clock frequency is specified, below which the device should operate satisfactorily.Flip Flop ApplicationsSerial Shift RegisterThe circuit below shows how data can be loaded into a serial shift register one bit at a time. This is a 4 bit register and so it would take four clock cycles to load a 4-bit number into the register.The timing diagram for this circuit (loading four 1s) is as follows:Notice how each JK flip flop transfers the“old”output from the previous FF because the propagation delay prevents them from seeing the “new” output because all FFs are clocked at the same time, or synchronously.EXAMPLE 4:For the serial shift register circuit above, draw the timing diagram as the 4-bit binary word 1011 is loaded.Parallel Shift RegisterThe circuit below shows how all data bits can be loaded from the parallel B inputs into the parallel Q register. This is a 4 bit register but it only takes one clock cycle to load the 4-bit number into the register.If the signal is inactive, the previously loaded data on Q3 – Q0 is always available no matter what is happening on the input lines B3 – B0. The advantage of this circuit is that while new inputs may present themselves at different times, they can be loaded synchronously to the output lines when the LOAD line is pulled LOW.Flip Flops Used in CountersIt will be seen in the following circuit that a FF operating in toggle mode is acting as a divide by two circuit and so frequency dividers and counters can be constructed from FFs in this mode.A 3-bit binary UP counterNotice that the JK control inputs are all tied to 5 V olts, which puts each of the FFs into toggle mode.EXAMPLE 5:For the 3-bit binary UP counter circuit above, draw the timing diagram for 10 clock cycles.EXAMPLE 6:For the 3-bit binary DOWN counter circuit below, draw the timing diagram for 10 clock cycles.DIGITAL ARITHMETICBinary Addition and SubtractionComputers use modified addition to perform subtraction and mulitiplication.Binary addition proceeds in the same manner as does decimal addition as is shown by the example below. The carries are shown is boxes.+1101100011 001000001011 1111100100EXAMPLE 7:Perform the binary addition below.+1100100111 00011101111101111 1110000010Signed NumbersIt is not easy to represent a + or – sign with a digital circuit and so an alternative is to use the MSBof a number to indicate whether it is positive or negative. The MSB is then the sign bit and the remainder of the number represents the magnitude. So for example, using a 0 to represent a positive number and a 1 to represent a negative number we could have the following:0 1001101 represents a positive number (MSB 0) of magnitude 10011012 = + 7710. Similarly:1 1001101 represents a negative number (MSB 1) of magnitude 10011012 = - 7710.The problem with using a system such as this is that the digital electronic circuits required to implement such a scheme are more complex than they need to be. For this reason we represent negative numbers using the 2’s-complement system.2’s-complement formFirstly, look at the 1’s complement of a binary number, which is formed by toggling all the bits in the number. For the 6-bit binary number 0001102(decimal 6) the 1’s complement is found by toggling all the bits:0001101's complement111001(all 1s to 0, all 0s to 1)So we say that the 1’s complement of 0001102 is 1110012. Then the 2’s complement of a binary number is found by adding 1 to the 1’s complement of that number. So for the example we used above, the 2’s complement of 0001102 is given by:000110 21's complement11100 1 2plus 1+ 1 1 22's complement111010 2The leading 1 means that the 6-bit number is negative and this bit contributes -25 = -3210 to the final result. The remaining bits sum to 2610, so the 2’s complement representation represents:-3210+2610 = -610.So taking the 2’s complement of the binary number representing + 610has yielded -610in 2’s complement notation.It is very important to note that we must be clear about how many bits we are working with. For example, if we are working with 6 bits, then 710 in binary is 0001112 which we would complement to form 1110002, however if we are working with 8 bits, then 710 would be represented as 000001112 which has a 1s complement of 111110002!So what are the limits to the numbers which can be represented in2’s complement form? Considering an n-bit number, the largest positive number we can represent will have a leading 0 followed by all 1’s. For example for 6 bits this number would look like:0111112 = 20 + 21 + 22 + 23 + 24 = 1 + 2 + 4 + 8 + 16 = 31 = 25-1.The largest negative number we can represent would have a leading 1 (to indicate it is negative) followed by all 0s. Again for a 6 bit number this would be:1000002 = - 25.More generally, the largest positive number which can be represented in n-bit 2’s complement notation is given by:2n-1 -1and the largest negative number which can be represented in n-bit 2’s complement notation is given by - 2n-1.As an example, represent the decimal number -2310in 2’s complement form using the minimum number of bits. The table below shows the minimum and maximum numbers (in decimal form) which can be represented in n-bit 2’s complement notation for n between 2 and 10.So to represent -2310 we need at least 6 bits.+2310 in 6-bit binary is:0101112and so the2’s complement of this binary number will represent - 2310.Taking the 2’s complement of 010111:01011 1 2101000 2+ 1 2101001 2Therefore our answer is:101001.Check: In 2’s complement notation:1010012 = -2510 + 10012 = -3210 + 910 = - 2310 as required.Would there have been any problem had we done all calculations using 8 bits instead of 6? Check this, and the 8-bit representation of +2310 is:000101112 and so the 2’s complement of this binary number should represent -2310.Taking the 2’s complement of 00010111:0001011 1 211101000 2+ 1 211101001 2Therefore our answer is:11101001.Check: In 2’s complement notation:111010012 = -2710 + 11010012 = -12810 + 10510 = - 2310 as required.EXAMPLE 8:Represent the number -7910 in 2’s complement notation using an 8-bit representation. + 7910 in 8-bit binary is given by 010011112.Taking the 2’s complement of 01001111:0100111 1 210110000 2+ 1 210110001 2Therefore our answer is:10110001.Check: In 2’s complement notation:101100012 = -2710 + 01100012= -12810 + 4910 = - 7910 as required.Addition and Subtraction Using Signed Binary NotationAdditionEach number must have the same number of bits and any carry in the result is discarded. The result will then be either:1. Correct2. Incorrect and +25610 larger than it should be or3. Incorrect and +25610 smaller than it should be.EXAMPLE 9:Add the two 8-bit signed binary numbers 011011112 (11110) and 001000002 (3210) together.+01101111 2 010******* 2 10001111 2This answer should be 11110 + 3210 = 14310. However the answer (remembering that it is in 8-bit signed binary form) is:.This is exactly 25610 less than it should be.Binary SubtractionIf we wish to calculate A – B we first find the 2’s complement of B (which is the negative of B) and then add it to A. We discard any carry which results from these operations.EXAMPLE 10:Using 8-bit signed binary notation, subtract 001000002 (3210) from 011011112 (11110). Confirm that the answer is 7910.Taking the 2’s complement of 001000002:00100000 2+1101111 1 2111111 211100000 2Add to 011011112 to give:+11100000 20111101111 2111111 2Discarding the carry we can see that this is the correct result.Binary MultiplicationThis proceeds in a way which is very similar to decimal multiplication. As an example, multiply 111001002 ( 22810) by 00001010 (1010). Confirm that the result is correct (228010).11100100 200001010 2+0000000111001000000000011111001001111100 2This binary number is in fact 228010.Arithmetic Circuits Half AdderThe 2-bit half adder circuit looks like:The truth table for this circuit is:CarryFull AdderWhile the half-adder can only add two bits together the full-adder can add together two words. Addition of the LSBs can result in a carry in, and addition of the next two bits (with the carry in) can lead to a carry out. The full-adder can manage these operations. A circuit which is capable of this operation is shown below.Counters and RegistersAsynchronous Ripple CountersAsynchronous DOWN and UP counters were introduced earlier. The figure below shows a 3-bit binary UP counter implemented using T FFs. The left most FF is changing its state most frequently and so the output is the LSB of the counter.We can draw the timing diagram for this circuit as follows.Notice that each flip flop divides the frequency by a factor of two.A state transition diagram shows us how the counter goes from state to state and an example from the circuit above is shown below.This counter has 8 possible states and it uses all of them. For such a simple counter when all states are being used we say the MODULUS of the counter is 2n where n is the number of FFs. In this case there are 3 FFs and so 8 states, as we have observed. However if we wish to design a counter with less states we will need some additional circuitry. One way to reduce the number of states is to detect a particular state and reset the counter.The NAND gate detects the two MSBs going high (as the circuit starts to enter the 110 state) and clears all FFs to 0. There will actually be a glitch in the timing diagram since the FFs have to start entering the 110 state momentarily before the conditions have been established to fire the NAND gate a clear all FFs. Our state diagram for this circuit is shown below. Notice that all possible states of the circuit are still shown, even though they are now not part of the normal count sequence.Notice also that the FFs do not change state at the same time, because there are propagation delays at each stage. Returning to the asynchronous ripple counter on page 28 and its timing diagram on page 29, if we look carefully at the transition from 111 to 000 we would see:If we look carefully at the transitions taking place as we go from 111 to 000 we see the following sequence:111110100000Including this set of transitions in a state diagram we have:If we wish to avoid these unwanted intermediate states we may need to add additional circuitry.Decoding Counter OutputsCounters can be used as timers and as such we need a means of detecting when a certain count has been reached. A decoding circuit does just this, generating an output when a certain count is detected. For a 4-bit counter there are 16 states, each one of which is different to the others. It is possible to therefore detect any one of the 16 states.EXAMPLE 11:Develop a circuit to decode the 5th count of a MOD 16 UP counter.The 5th state is 01012 and so a suitable circuit could look like:Decoding AddressesWe may wish to select a particular address on a 16 bit address bus from all the possible addresses.A similar circuit as that shown above can be used for this task.EXAMPLE 12:Develop a circuit to decode the address 4590510 from a 16-bit address bus.First we need to convert 4590510 to binary. We can use repeated division as follows:22952 remainder of122952 ÷ 2 11476 remainder of011476 ÷ 2 5738 remainder of05738 ÷ 2 2869 remainder of02869 ÷ 2 1434 remainder of11434 ÷ 2 717 remainder of0717 ÷ 2 358 remainder of 1358 ÷ 2 179 remainder of0179 ÷ 2 89 remainder of189 ÷ 2 44 remainder of144 ÷ 2 22 remainder of022 ÷ 2 11 remainder of011 ÷ 2 5 remainder of15 ÷ 2 2 remainder of12 ÷ 2 1 remainder of01 ÷2 0 remainder of1The binary equivalent of 4590510is therefore 10110011010100012. A circuit which decodes this address is therefore as shown below. Notice that all 16 inputs to the NAND gate are set to one, the only condition which will create a zero at the NAND gate output.Some Medium Scale Integrated Circuit DevicesEncodersThis device takes any one of a number of possible inputs and outputs a code to represent that input.A generalised structure for an encoder is:Note that:.DecodersInputs N-bits of coded data and activates one of M outputs. A generalised decoder is shown below.MultiplexersThese devices select one of a number of input lines and put the data on that line through to the output. These are also called MUXs and can be thought of as a digital multi-position switch. A generalised MUX is shown below.The control inputs , and determine which input will be passed to the output.DemultiplexerA demultiplexer (DEMUX) takes a single input and distributes is to one of several outputs. A generalised DEMUX is shown below. The control inputs , and determine to which outputthe input is passed.MODULE 9 PRACTICE TEST1.The timing diagram below shows the inputs to the and terminals of an SR latch. Alsoshown is the starting state of the circuit ( and ). Complete the and outputsfor the timing diagram.plete the truth table for the circuit below, showing all possible combinations of and, and and the role of each combination.。

1995年Passage l Money spent on advertising is money spent as well as any I know of. It serves directly to assist a rapid distribution of goods at reasonable price, thereby establishing a firm home market and so making it possible to provide for export at competitive prices. By drawing attention to new ideas it helps enormously to raise standards of living. By helping to increase demand it ensures an increased need for labour, and is therefore an effective way to fight unemployment. It lowers the costs of many services: without advertisements your daily newspaper would cost four times as much, the price of your television license would need to be doubled, and travel by bus or tube would cost 20 per cent more. And perhaps most important of all, advertising provides a guarantee of reasonable value in the products and services you buy. Apart from the fact that twenty-seven acts of Parliament govern the terms of advertising, no regular advertiser dare promote a product that fails to live up to the promise of his advertisements. He might fool some people for a little while through misleading advertising. He will not do so for long, for mercifully the public has the good sense not to buy the inferior article more than once. If you see an article consistently advertised, it is the surest proof I know that the article does what is claimed for it , and that it represents good value. Advertising does more for the material benefit of the community than any other force I can think of. There is one more point I feel I ought to touch on. Recently I heard a well-known television personality declare that he was against advertising because it persuades rather than informs. He was drawing excessively fine distinctions. Of course advertising seeks to persuade. If its message were confined merely to information-and that in itself would be difficult if not impossible to achieve, for even a detail such as the choice of the colour of a shirt is subtly persuasive----advertising would be so boring that no one would pay any attention. But perhaps that is what the well-known television personality wants. 51. By the first sentence of the passage the author means that__. [A] he is fairly familiar with the cost of advertising [B] everybody knows well that advertising is money consuming [C] advertising costs money like everything else [D] it is worthwhile to spend money on advertising [答案] C [解题思路] 本题可以直接从分析该句的⾓度解题。

Unit 4 History and Traditions 单元分析本单元主题：人与社会﹣﹣历史、文化与传统一、单元内容分析本单元以历史与传统为话题，围绕中国、英国和爱尔兰等国家的悠久历史和文化传统展开，内容涉及历史遗迹和国家历史概况，通过景物描写表达的深层含义和作者情感，以及分享观光旅游的经历，引领青少年了解中国、英国、爱尔兰、墨西哥等多个国家的悠久历史和文化传统，积极思考历史文化与传统的重要性及现实意义。

旨在让青少年能够结合自己的生活和学习需要及相关历史文化知识等，观察和分析语言和文化现象，了解相关国家悠久历史和特色传统的文化内涵和现实意义，思考历史与现实的辩证关系。

以下为教材各部分教学内容简要分析及教学活动实施建议：1.Opening Page 主题图展示的流经伦敦的泰晤士河及其岸边的重要建筑群，集中体现了英国的历史文化风貌，是英国历史、地理、人文、建筑艺术等方面的一个缩影。

开篇页的引言" A people without the knowledge of their past history , origin and culture is like a tree without roots ."即"一个不了解自己历史、起源和文化的民族，就如同一棵无根之树"。

通过类比，阐释了历史起源及其所蕴含文化的重要性。

2.Listening and Speaking : Share views on historic sites 外国游客的视角，描写他们对孔子这位对中国历史与文化传统产生深刻影响的伟大人物的好奇、仰慕和喜爱，并由孔子后人Xiao Kong 来介绍有关孔子后裔及其教育思想等方面的情况，语境创设真实，容易引起学生的兴趣和共鸣。

在对话中，William 用到了Achilles ' heel 、pull one ' s leg 、fish out of water 等英语习语和典故，并由一个城市建筑限高的细节，联想到自己的故乡﹣﹣埃文河畔的斯特拉特福，从而引出英国伟大的剧作家莎士比亚，既体现了语言、文化、历史、传统的有机结合，又反映出中英两国对历史与传统的尊重与保护，同时也为后面板块中与英国相关内容的学习进行预热和铺垫。

诗歌中caesurae的例子(一)诗歌中的Caesurae什么是Caesurae？Caesurae（中文译为“断句”）是指诗歌中的一种停顿或断行方式。

它在诗歌中起到分割、强调和节奏的作用。

在英文诗歌中，通常指两个强重音之间的断句，而在古代拉丁诗歌和一些其他语言的诗歌中，断句可以出现在句子的任何位置。

例子及讲解以下是一些常见的Caesurae（断句）的例子，并对它们的作用进行详细讲解：•例子 1:“To err is human, to forgive divine.”在这个例子中，短语“is human”和“to forgive”之间的逗号（，）可以被视为一个Caesurae。

它在诗歌中创造了一个停顿，强调了“is human”和“to forgive”这两个重要的概念。

这样的断句也有助于划分诗句的韵律和节奏。

•例子 2:“Not enjoyment, and not sorrow, Is our destined end or way.”在这个例子中，逗号（，）在“Not enjoyment”和“and not sorrow”之间形成了一个断句。

它创造了一个明显的停顿，使得读者可以更好地理解并强调“Not enjoyment”和“and not sorrow”这两个概念。

•例子 3:“And the night is a-cold; And the night is a-cold;在这个例子中，分号（;）在两个相同的词组之间形成了一个断句。

这种断句的作用是强调并重复前半部分的词组，从而在诗歌中创造出一种复杂的韵律和节奏。

•例子 4:“O, what a noble mind is here o’erthrown!”在这个例子中，感叹词“O”和逗号（，）之间形成了一个断句。

这个断句用于强调和加重“what a noble mind is here o’erthrown”这个表达。

•例子 5:“I wandered lonely as a cloud That floats on high o’er vales and hills.”在这个例子中，两行诗之间的断行可以被视为一种断句。

U8P.62 2b课文翻译巨石阵---谁能解释它的存在巨石阵,一个岩石圈,不仅是英国最着名的历史古迹之一,而且它是其中一个最大的谜团.每年接待了超过75万游客.特别是在6月,人们很喜欢去这个地方,因为他们想看到一年中最长的一天看日出.许多年以来,历史学家认为巨石阵是古代领导人试图与神沟通一座寺庙.然而,历史学家保罗斯托克认为这不可能是真的,因为巨石阵建造于很多世纪以前.“这些领导人抵达英国晚得多.”他指出.另一个普遍的观点是,巨石阵可能是一种日历.这些巨石以一种的独特的方式被放置在一起.在仲夏的早晨,阳光直接照射石头的中心.其他人认为,这些石头有一种医学的目的.他们认为这些石头能够预防疾病,同时保持人们身体健康.”当你走到那儿时,你可以感觉到能量从你的脚传上你的身体,”一位游客说.没人确信巨石阵是什么用途,但大多数赞同石头的位置必定有一个特殊目的.有些人认为它可能是一个埋葬先人的地方,或是一个纪念祖先的地方.其他人认为它是庆祝战胜敌人而建的.巨石阵是历经一段很长的时期被慢慢建成的.大多数历史学家认为它年龄一定接近5000岁.最伟大的奥秘之一是它是如何被建造,因为石头太那么大又那么重.2001年,一群英国志愿者试图构建另一个巨石阵,但他们没能做到.“我们真的不知道是谁建造了巨石阵,”保罗·斯托克说.”,也许我们可能永远不知道,但我们知道他们一定是很勤奋---而且是伟大的规划者”课文重难点讲解：E.g.1. As it is snowing从句, we shall not go to the park主句.2.---Why were you absent from school yesterday---Because I was ill in bed.On that day I was absent from the meeting 主句because I was in Guangzhou从句.3.Since everyone is here,let’s begin the discussion.II.Circle 可数名词,意为“圆圈”,也可表示具有共同兴趣爱好或职业等的“阶层；圈子；界”.e.g.The children stood in a circle around the fire.The man is well-known in historical circles.Circle 还有动词的意思,表示“圈出”.Please circle the correct answer.III.receive 及物动词,此句中意为“接待；招待”.recieve 还可以表示“接受；收到”, 与get 同义,其后可接介词 from.They are very glad to have the opportunity to receive the quest.I received a letter from my mother this morning.Receive和accept辨析,两者都有收到的意思,但用法不同1.receive强调客观上收到这一事实,不表明是否愿意接受.2.accept主动地或自愿地接受,带有“满意；同意；认可”等意味,其反义词为refuse.e.g.I receive his invitation to the party yesterday, but I refuse to accept it. The docter received a threating letter.The teacher accepts the naughty student,Molly’s apology.IV.medical 形容词,意为“医疗的；医学的”其名词形式是 medicine.He is a medical student.他是个医科学生.Have you taken your medicine this morning今天早上你吃过药了么V.purpose 名词,意为“目的；目标,意图”, 常与of 连用构成the purpose of. 常见短语 on purpose, 意为“故意地”What was the purpose of his visitHe came here for/with the purpose of seeing his family.Li Ming broke the windows on purpose.VI.prevent/stop sb.from doing sth. 意为“阻止某人做某事”.My mother prevents/stops me from eating too much candies.We should prevent the water from being polluted.注意：from 在主动语态中可以省略,但在被动语态中不得省略.He was prevented/stopped from playing computer games on school nights. VII. energy 意为"精力；力量",不可数名词Young people usually have more energy than the old.年轻人通常比老年人更有活力.VIII.celebrate Vt.庆祝其名词形式是celebrationWe held a party to celebrate the School Day.The woman is always mysterious.Her past is a mystery.。

考研英语阅读题的解题方法：例证题方法讲解考研英语阅读题的解题方法：例证题方法讲解导语：考研英语阅读是整体试卷分数最重的部分，历年都是兵家必争之地，也是让很多考生很“忧愁”的题型之一。

下面是小编为您收集整理了、考研英语关于例证题的方法讲解，欢迎阅读!例证题方法讲解一、判断题型通过对考研英语阅读文章题干的观察分类例证题题干特点如下，当题干中出现example，demonstrate，illustrate，case，story等词即可判断该题干为例证题，见历年真题题干如下：1. Wilt Chamberlain is cited as an example to____. (2008 text3)2. George Washington's dental surgery in mentioned to____. (2008 text 4)3. The birthday phenomenon found among soccer players is mentioned to____. (2007 text 1)4. The statement “It never rains but it pours” is used to introduce____. (2007 text 4)例证题方法讲解二、错误选项特点通过对真题的分析，例证题错误选项的特征多为就事论事，混淆论点论据。

见真题如下：1. The extinction of large prehistoric animals is noted to suggest that_____. (2006 Text 3)[A] large animal were vulnerable to the changingenvironment(文中一段例子中的细节，不可概括主题)[B] small species survived as large animals disappeared(文中一段例子中的细节，不可概括主题)[C] large sea animals may face the same threat today[D] slow-growing fish outlive fast-growing ones(与文中一段三句相矛盾，属于一段例子中的细节上的反向干扰。

文章标题：探寻afntharedrg的中文1. afntharedrg的中文起源在探究afntharedrg的中文之前，首先要了解afntharedrg这个词的来历。

afntharedrg一词最早可以追溯到古代文明，它在当时的语境中有着独特的意义和象征。

afntharedrg在中文中的表达由来已久，并且在不同的历史阶段都有着不同的内涵和解读。

2. afntharedrg的中文解读与内涵在现代社会中，对于afntharedrg的中文理解已经有了新的发展和演变。

我们不仅要了解其历史渊源，还要深入挖掘其在当代语境中的意义。

afntharedrg的中文所蕴含的内涵和象征意义，对于当代社会风气的影响和人们内心世界的塑造有着重要的启示和作用。

3. afntharedrg的中文在当代社会中的应用afntharedrg的中文在当代社会中有着广泛的应用，在不同领域和行业中都可以看到其身影。

从文化传承到商业运作，afntharedrg的中文都发挥着重要的作用，并且与时俱进地展现着其活力和魅力。

探索afntharedrg的中文在当代社会中的应用，可以帮助我们更好地理解并把握当下的社会脉搏。

4. 个人对afntharedrg的中文的理解对于afntharedrg的中文，每个人都有着自己独特的理解和认识。

afntharedrg的中文对我而言，不仅是一种语言表达，更是一种精神追求和人生态度。

通过对afntharedrg的中文的探寻和思考，我对自己的内心世界有了更深刻的认识，也激发了我对生活更加热爱和向往。

5. 总结与回顾afntharedrg的中文是一个值得深入探讨的话题。

通过对afntharedrg 的中文的深入理解和探寻，我们可以更好地认识自己，理解世界，拓展人生的广度和深度。

afntharedrg的中文如同一扇扇通向内心深处的窗，透过它，我们可以看到更丰富、更立体的世界。

希望我的文章能够帮助你更加深刻地理解afntharedrg的中文，以及文化、历史和当代社会背后的丰富内涵。