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The QSO evolution derived from the HBQS and other complete QSO surveys

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a r X i v :a s t r o -p h /9612181v 1 18 D e c 1996The QSO evolution derived from the HBQSand other complete QSO surveys 1Fabio La FrancaDipartimento di Fisica,Universit`a degli studi “Roma TRE”Via della Vasca Navale 84,I-00146Roma,Italy Electronic mail:lafranca@astrpd.pd.astro.itandStefano CristianiDipartimento di Astronomia,Universit`a degli studi di PadovaVicolo dell’Osservatorio 5,I-35122Padova,Italy Electronic mail:cristiani@astrpd.pd.astro.itSubmitted to the The Astronomical JournalABSTRACTAn Homogeneous Bright QSO Survey (HBQS)has been carried out in the framework of an ESO Key programme.327QSOs (with M B <−23and 0.3<z <2.2)have been selected over an area of 555deg 2in the magnitude range 15<B <18.75.For magnitudes brighter than B =16.4the QSO surface density turns out to be a factor 2.2higher thanwhat measured by the PG survey,corresponding to a surface density of 0.013+.007−.005deg −2.If the data from the Edinburgh QSO Survey are included,an overdensity of a factor 2.7is observed,corresponding to a surface density of 0.016±0.005deg −2.In order to derive the QSO optical luminosity function we used Monte Carlo simulations that take into account of the selection criteria,photometric errors and QSO spectral slope distribution.We have combined our data with the Edinburgh QSO Survey,the Large Bright QSO Survey,Durham/AAT survey,ESO/AAT faint survey and the (ZM)2B survey.The luminosity function can be represented with a Pure Luminosity Evolution,L (z )∝(1+z )k ,of a two power-law both for q 0=0.5and q 0=0.1.For q 0=0.5the k evolution parameter is k =3.26±0.07,slower than the previous Boyle’s (1992)estimate k =3.45.A flatter slope β=−3.72±0.13of the bright part of the luminosity function is also required.If a spread in the QSO spectral slope of σγ=0.3and 0.5is taken into account,the k parameter drops to 3.2and 3.0respectively.The observed over-density of bright QSOs is concentrated at redshifts lower than 0.6.It results that in the range 0.3<z <0.6the luminosity function is flatter than observed at higher redshifts.In this redshift range,for M B<−25,32QSOs are observed instead of19expected from our best-fit PLE model.This feature requires a luminosity dependent luminosity evolution in order to adequately represent the data in the whole0.3<z<2.2redshift interval.The observed overdensity of low redshift bright QSOs could be originated by the contribution of a slower evolving population of radio-loud QSOs.Subject headings:159-Quasi-stellar Objects1.INTRODUCTIONThe study of the evolution of the QSO Luminosity Function(LF)is of primary importance in order to understand the physic driving the central”engine”of AGNs(e.g.Efstathiou&Rees1988,Haehnelt &Rees1993).Studies of the large scale structure of the Universe(e.g.Andreani&Cristiani1993), and of the extragalactic X-ray and UV background (e.g.Madau,Ghisellini&Fabian1994;Comastri et al.1995;Haardt&Madau1996)are based on the knowledge of the optical QSO LF and its relationship with other wavebands.The LF of the optically se-lected QSOs is also the starting point to disentangle the evolutionary properties of the two populations of the radio-loud and radio-quiet QSOs(La Franca et al. 1994).The general behaviour of the LF is fairly well es-tablished in the redshift interval0.3<z<2.2 for which color techniques provide reliable selection methods(see Hartwick and Schade(1990),Boyle (1992)and Hewett and Foltz(1994)for a review of the subject).The prevailing model was proposed by Boyle,Shanks&Peterson(1988)and was based on a sample of420faint(b<20.9)AGNs,combined with the Palomar Green(PG)Bright QSO Sample (BQS,Schmidt&Green1983)consisting of92QSOs with B<16.4.The model consists of a double-power-law shape invariant with redshift,with a steep bright end dN/dL∝L−3.9,and aflatter faint end dN/dL∝L−1.5.The evolution is simply represented by the so-called Pure Luminosity Evolution(PLE)in which the characteristic luminosity(L∗)of the break between the two power-laws evolves as a function of redshift according to L∗(z)∝(1+z)3.4.In the last years a number of papers have been published suggesting that the standard two power-law model in the framework of a pure luminosity evolution may not be an adequate representation of the data (Goldschmidt et al.1992;Miller et al.1993;Hewett, Foltz&Chaffee1993;Hawkins&Veron1995).The most controversial points are the amount offlattening of the faint part of the LF,first discovered by Boyle et al.(1988),and the shape of the bright part which, in the last decade,has been based almost entirely on the PG bright QSO survey data.In this paper we present a new determination of the QSO LF and its evolution.We devote special care to the shape of the bright part of the LF,for which we have derived new data from a bright QSO sam-ple:the Homogeneous Bright QSO Survey(HBQS, partly published in Cristiani et al.1995).In the computation we take also into account the most rele-vant already existing QSO samples,in particular two new bright QSO surveys:the Edinburgh QSO Sur-vey(EQS,Goldschmidt et al.1992),and the Large Bright QSO Survey(LBQS;Hewett,Foltz&Chaffee 1995and references therein).2.THE SAMPLESAs discussed in section4,we have used Monte Carlo simulations in order to derive the bestfit QSO LF.For this reason our analysis is mainly based on a set of QSO samples for which the selection criteria and the photometric properties are well defined or at least can be acceptably reproduced.In addition to the knowledge of the K-correction and QSO colors, for a rigorous determination of the LF we need the definition for each sample of:•theflux limits and selection criteria;•the distribution of the photometric errors as afunction of apparent magnitudes;•the galactic absorption;•the color equations of the photometric system.The QSO LF will be computed in the Johnson B absolute magnitudes.In the following color equations the“natural”photometric systems are marked with primed letters,while the Johnson/Cousins system is represented with unprimed letters.2.1.The HBQSThe Homogeneous Bright QSO Survey(HBQS) was started in1989in the framework of an ESO Key-programme.The survey covers a total of555deg2 subdivided in22ESO/Schmidt or UKSTfields at high galactic latitude around the south galactic pole (b<−60◦).Two Schmidt plates for each bandpass U(IIa-O +UG1or IIIa-J+UG1),B′(IIa-O+GG385)or B J(IIIa-J+GG395),V′(IIa-D+GG495),R(IIIa-F+RG630)or OR(IIIa-F+OG590),and I(IV-N+RG715)have been obtained at the UKST or ESO/Schmidt telescope,usually within a few months interval,in order to minimize the effects of variability. The plate material has been scanned on the COSMOS microdensitometer.The resulting tables,containingthe instrumental magnitudes and other useful param-eters for the objects detected in each plate,have been merged together in one table perfield.Only ob-jects with at least4detections(in10plates)have been included in thisfinal table.According to the ESO/UKSTU numeration,the13ESOfields which have been selected in the B′photometric system are: 290,349,355,406,407,408,410,468,469,470,474, 479,534.The9UKSTfields which have been selected in the B J photometric system are:287,295,296,297, 351,411,413,SA94,SGP.We have selected as candidates all the UVx“not-extremely-extended”objects satisfying a type of mod-ified Braccesi less-restricted two-color criterion(La Franca,Cristiani&Barbieri1992).The principal color for the selection has been chosen to be the U−B′or the U−B J according to the type of the available plate material.The secondary color has been chosen to be B J−R or B J−V′or B′−V′,always preferring the combination giving the most reliable photometric accuracy.The adopted color equations(Blair&Gilmore 1982)are,for the B′(IIa-O+GG385)system:B=B′+0.11(B−V);while for the B′J(IIIa-J+GG395)system:B=B′J+0.28(B−V)(1) The magnitude intervals in which the selection is virtually complete vary fromfield tofield between 15.0<B<17.3and15.0<B<18.8.The sample extracted from these data includes327QSOs (M B<−23,q0=0.5,and H0=50Km/s/Mpc). Cristiani et al.(1995)describe in detail the pro-cedure followed in the data acquisition and reduc-tion and report thefirst results obtained in sixfields (∼150deg2,the ones reaching fainter limiting mag-nitudes),providing significant statistics in the range (16.75<B<18.75).2.2.The Edinburgh QSO Survey(EQS)The Edinburgh bright UVx QSO Survey(EQS)has been carried out over13UKSTfields(the area is333 deg2large)with the UB J V RI multicolor system(see Goldschmidt et al.1992).The data reduction was very similar to that of the HBQS.The photometric rms errors are of0.09mag in each bandpass in the magnitude interval15<B<18were most of the QSOs are.The selection criteria is fairly well repre-sented by the equations:U−B J<−0.35and B J−R>0.The intervals of magnitude for which a reliable sample can be extracted vary from15.0<B<17.5to 15.0<B<18.5in the differentfields(Goldschmidt 1994).For our computation of the LF we have used the bright(B<16.5)subsample of8QSOs with z>0.3published by Goldschmidt et al.(1992).In this subsample the AGN with b=15.79and z=0.380 has been excluded because of a wrong redshift iden-tification(Goldschmidt1994).2.3.The LBQSThe Large Bright QSO Survey covers an effective area of454deg2(Hewett,Foltz and Chaffee1995and references therein).The photometry has been carried out in the B J bandpass and the errors are on aver-age of0.10magnitudes,taking also into account zero point errors and variations across UKSTfields.The sample is based on1055QSOs and AGNs,with ap-parent magnitudes in the range16.5<B J<18.85 and redshifts in the range0.2<z<3.4.The se-lection has been carried using objective prism plates, looking for emission line and/or blue continuum ob-jects.Because of the selection of the blue continuum objects the sample is complete in the redshift range 0.2<z<2.2.It is not possible to directly simulate the selection criteria of this survey,however in order to check the effects in the LF by the inclusion of such a large database,we have temptatively simulated the blue continuum selection as an UVx selection:U−B J<−0.30.As for the EQS and HBQS samples the adopted color equation is(1).In our computation of the LF we have restricted the LBQS to a subsample of220QSOs in the magnitude range16.5<B<18.0.2.4.The SA94SurveyThe SA94survey is an UVx(UBV)selected sample over an area of10deg2.The QSOs have been selected according to the less restricted Braccesi UVx criterion (La Franca et al.1992).The completeness magnitude range is15.0<B<19.9.The complete sample ex-tracted from the data includes97QSOs.The B mag-nitudes are directly published in the Johnson/Cousins system and no color transformation is needed.2.5.The Durham/AAT SurveyThis sample comes from an UVx stellar object se-lection from UK Schmidt U and B J plates.The B Jplates have been calibrated on the B magnitude sys-tem.Therefore the magnitudes of this surveys are referred as b magnitudes for which the color equation is(Boyle et al.1990):B=b+0.23(B−V−0.9).The whole catalogue containing420AGNs is sub-divided in34circularfields having a diameter of40′, corresponding to a total area of11.9deg2.The com-pleteness magnitude ranges vary fromfield tofield, the faintest limit magnitude reaching b=20.9.Dif-ferent UVx selection limits have also been adopted in the variousfields(see Boyle et al.1990,Table2).On average they correspond to u−b<−0.40.In the red-shift interval0.3<z<2.2the sample consists of353 QSOs.2.6.The ESO/AATThis is a faint UJRI survey of66AGNs in the fields855,861,864(Boyle,Jones and Shanks1991), where J′is a IIIa-J+GG385system.The color equa-tion is(Kron1980):B=J′+0.23(B−V).The survey covers an effective area of0.85deg2from J=18.0down to J=21.75−22.0,and the complete-ness redshift range is0.6<z<2.9.The typical rms scatter in the calibration is0.09mag for the J band-pass,0.15mag for R passband,and0.12mag in the U bandpass.The candidates were selected among all the stellar objects lying blueward of the stellar locus in either U−J or J−R diagrams.At z<2.2the subsample consists of41QSOs whose selection is well represented withU−J<−0.30.2.7.The(ZM)2B SurveyThis is a faint UVX survey of54AGNs from UJF plates taken at the ESO3.6m telescope(Zitelli et al. 1992).The survey cover an area of0.69deg2down to J=20.85and0.35deg2down to J=22.0.In the redshift range0.3<z<2.2the complete sample consists of19QSOs.The selection criterion is well represented byU−J<−0.30.Fig.1.—The QSO number counts for0.3<z<2.2. The continuous line represents the bestfit LDLE model(model C in Table2),the dashed line rep-resents our bestfit PLE model(model B in Table 2),while the dotted line represents the bestfit PLE model(model A in Table2)by Boyle et al.(1992). The magnitudes have all been corrected for galactic extinction according to Burstein and Heiles(1982). As in the previous survey the color equation is:B=J′+0.23(B−V).3.THE QSO COUNTSThe B number-magnitude counts for all the sam-ples used in the computation of the optical LF are shown in Fig. 1.In the following we will re-strict our analysis to0.3<z<2.2because this is the only interval in which the selection criteria allow a reliable and homogeneous processing of the data.The magnitudes have all been corrected for galactic extinction according to Burstein&Heiles (1982).The QSO surface densities from the HBQS and EQS are also shown in Table1.Asfirst in-dicated by Goldschmidt et al.(1992),for magni-tudes brighter than B=16.4the QSO surface den-sity turns out to be a factor2.5higher than what measured by the PG survey(Schmidt&Green1983).The data from the HBQS collect7QSOs at mag-nitudes brighter than B=16.4,corresponding to asurface density of0.013+.007−.005deg−2.With the ad-dition of the EQS,the surface density at B<16.4 becomes0.016±0.005deg−2,corresponding to a to-tal of14QSOs over an area of888deg2.The PG sample lists44QSOs at B<16.4.In this range the surveyed area changes rapidly as a function of the limiting bining the number of dis-covered QSOs with the areas according to Table1of Green,Schmidt&Liebert(1986),a QSO surface den-sity of0.006±0.001deg−1is obtained,a factor of2.7 lower(significant at2σlevel)than the EQS+HBQS estimate.The presence of incompleteness in the PG survey has been investigated by Wampler and Ponz (1985).It probably originates for QSOs with U−B colors near the selection limit because of large rms errors.This effect would lead to incompleteness that varies with redshift,with the consequence that,in particular in the range0.4<z<0.7,it is system-atically underpopulated at a given magnitude.This hypothesis appears corroborated by the fact that the PG survey,in the area covered to a limit B=16.4, has discovered46QSOs with z<0.3,in addition to the44with z>0.3that are relevant for the compar-ison with the current sample.For these reasons we have excluded the PG sample from our subsequent analysis of the evolution of the LF.At fainter mag-nitudes,in the interval16.5<B<18.5,the HBQS shows a fairly good agreement with the counts of the LBQS.4.THE LUMINOSITY FUNCTION4.1.Deterministic DerivationsThe QSO LFΦ(M,z)is the measure of the number of QSOs per unit of commoving volume with magni-tudes in the interval(M,M+dM)as a function of redshift z.In the redshift interval0.3<z<2.2the general behaviour of the QSO LF has been usually parameterized with a double power-law Pure Lumi-nosity Evolution(PLE)modelΦ(M B,z)=Φ∗if the extrapolation is large,it is important toknow the spread of the distribution ofγ.Anydistribution of the mean spectral index is re-flected in an uncertainty in the absolute magni-tudes,which increases with redshift and intro-duces an artificial luminosity evolution of thepopulation.The dispersion in the power-law in-dexγin the rest-frame ultraviolet is substantial(Sargent,Steidel and Boksenberg1989;Franciset al.1991;Schneider et al.1991),with esti-mates ofσγ=0.3−0.6.For a sample of QSOsmeasured at the same observed wavelength thedifferential effect between two redshifts z1,z2is ∆M B=2.5∆γlog[(1+z2)/(1+z1)].In the redshift range of our analysis0.3<z<2.2,changing from z=0.3to z=2.2results in auncertaintyσMB≃σγ.A value∆γ=0.5would correspond to an error in the space density of afactor3in the bright part of the LF assuminga power-law indexβ=−3.5.In the case oftwo QSOs of the same redshift and apparentmagnitude B but different spectral index,thedifference in absolute magnitude is∆M B=2.5∆γlog(1+z).Changing fromγ=0toγ=1.5would produceat z=0.4a difference in absolute magnitudeof∆M B=0.4mag.At z=2.2the differencebecomes1.9mag corresponding to an error inthe space density of a factor100in the brightpart of the LF(assuming a power law indexβ=−3.5).Thefinal result of this effect is ablurring of the LF.The“standard”maximum likelihood techniques (Marshall et al.1983,Boyle,Shanks and Peterson 1988)do not need binning of the data and overcome the disadvantage described in item(1),but do not solve problems(2)and(3).In order to take into account also these latter two effects,it has been proposed to compute a detection probability as a function of apparent magnitude,red-shift and Spectral Energy Distribution(SED)(see Warren,Hewett&Osmer1994).The detection prob-ability p(m,z,SED)is derived computing the frac-tion of QSOs that would have been selected by each survey according to the selection criteria,photometric errors,and the spectral index.Thus,for each redshift and magnitude interval,the space density is evaluated asΣ1/ p(z)dV a.Eventually,in order to determine the range of parametric luminosity-function models that are consistent to the data,the observed and ex-pected number of QSOs are compared through max-imum likelihood or leastχ2techniques.4.2.The Monte Carlo SimulationsThe above described procedures do not lead to a fully satisfactory and rigorous determination of the LF.The photometric errors and the spread in the QSO SED properties make the nature of the prob-lem intrinsically stochastic.Even taking into account the influence of different SEDs in the computation of the absolute luminosity,the problem remains ba-sically unsolved.For example,because of the effects of the photometric errors,two QSOs observed at the same apparent magnitude and with the same SED and redshift may be produced by objects of different absolute magnitudes.This means that it is impossi-ble to establish a bi-unique(one-to-one)relationship between the observed apparent magnitudes and the absolute magnitudes as a function of z and SED.For these reasons we have followed a different ap-proach,simulating,with Monte Carlo techniques, what happens when a selection of a sample is made. For each sample the following procedure has been ap-plied:1.Assuming a theoretical LF distributionΦ(M B,z),a number(proportional to the surface area ofthe survey)of QSOs(i.e.pairs M B,z)havebeen randomly extracted;2.The apparent magnitudes of the QSOs havebeen computed following the K-correction ac-cording to Cristiani&Vio(1990),and derivingthe average galactic absorption A B from the HImaps of Burstein and Heiles(1982).The result-ing apparent B magnitude is:B=M B+5log[A(z)c/H0]+25+K(z)+A B+ǫ(B)whereǫ(B)simulates a noise with Gaussian dis-tribution with varianceσ2B=σ2phot(B)+σ2B,γ.σ2B takes into account both the photometric er-rors of the surveyσphot(B)and the apparentmagnitude dispersion due to the QSO spectral slope dispersionσγσB,γ=2.5σγlog(1+z).3.The apparent colors have been generated follow-ing the average QSO colors-redshift dependence F1,2(z)(Cristiani&Vio1990).Between each couple of bandpasses centered atλ1andλ2the resulting apparent color is:C1,2=F1,2(z)+ǫF1,2whereǫF1,2simulates a noise with Gaussian dis-tribution with varianceσ2F1,2=σ21+σ22+σ2F,γ.σ2F1,2takes into account the photometric errorsof the two bandpassσ1andσ2respectively,and the QSO color dispersion due to the spreadσγin the slope of the spectraσF,γ=2.5σγlogλ2Smirnov(2D KS)test by Fasano and Franceschini (1988).See Press et al.(1992)for a complete de-scription of the algorithm.In the following wefirst focus our discussion on a q o=0.5universe,we will later see how our results change for q o=0.1.In Fig.2our bestfit PLE model(B)is shown.The data points,representing the estimates of the QSO space densities,are compared to thefitted LF.The observed QSO space densities have not been directly computed through the1/V a technique,that,due to the binning of the data,can give origin to spurious trends on the shape of the LF(see sub-section4.1). For this reason we have preferred to exploit our Monte Carlo simulation code in order to visualize the LF. The value of each observational point in Fig.2has been computed by comparing,in each absolute mag-nitude/redshift bin,the number of observed QSOs, N o,with the number of QSOs simulated with thefit-ting LF,N s.Let us callΦo andΦs the corresponding luminosity functions andΨ(M,z)the selection func-tion.In each bin we have:N o,Ψ(M,z)Φs(M,z)dMdzwhere the integrals are computed over the correspond-ing bin.In our case,in each bin,we can assume that the shape of the observed andfitting LFs are very similar,apart from a constant factor k,which varies from bin to bin:Φs≃kΦing this assumption we can write:N o,Φs(M,z)for all values M and z in the bin.Consequently,for proper visualization of the data,the observed QSO densities have been computed by multiplying the cor-responding value of the simulating LF,Φs,at the cen-tral magnitude and redshift of the bin,by the ratio between the number of observed and simulated QSOs in the corresponding bin:N oΦo(M,z)≃mined by Boyle(1992)is a result of the introduction of the redshift cut offat z cut=1.9,which with our data results unnecessary.Both A and B models provide an inadequate sim-ulation of the distributions of the observed data for the low redshift domain,0.3<z<0.6.For this subsample the2D KS statistics test rejects model A at the0.01level and model B at0.02level.At magnitudes brighter than M B=−25,in the interval 0.3<z<0.6,32QSOs are observed,while16and19 QSOs are predicted by model A(a4σdiscrepancy) and B(a3σdiscrepancy)respectively.But as the low redshift(z<0.6)subsample contain only5per cent of the complete data set,in a global comparison of the whole data sample in the interval0.3<z<2.2,the models follow the evolution of the larger fraction of QSOs at higher redshift,allowing theχ2probability of the globalfit to reach satisfactory levels.No significant difference is obtained byfitting the data excluding each of the three bright samples(HBQS, EQS and LBQS)in turn(models D,E and F).It is interesting to see how the inclusion of a spread in the theoretical average QSO spectral slope modifies the bestfit luminosity function.As expected(Gial-longo and Vagnetti1992),larger values of the spread of the slope correspond to slower luminosity evolution parameters and steeper luminosity functions(model G withσγ=0.3,and model H withσγ=0.5).In order to fully represent the data in the redshift range0.3<z<2.2we tried several functional mod-ifications of the PLE.Asfirst step we tried,without significant results,to add one or at maximum two pa-rameters in order to take into account of a dependence of the bright slopeβwith redshift.The best description of the observed data has been obtained by decreasing at low redshift the luminosity evolution of the bright QSOs.This has been obtained by including a dependence on the redshift and abso-lute magnitude of the evolution parameter k such as:for M B≤M∗:k=k1+k2(M B−M∗)e−z/.40(2) for M B>M∗:k=k1where M∗is the magnitude of the break in the two power-law shape of the LF.This luminosity depen-dent luminosity evolution(LDLE)model(model C in Table1)has resulted in a betterfit of the data(see Fig.3)giving aχ2test probability of0.49in the whole B,z plane,and an acceptable2D KS proba-bility of0.09in the redshift interval0.3<z<0.6.Fig.3.—The QSO luminosity function.The points connected with a continuous line represent the obser-vations(see text for details about their derivation). The dashed lines correspond to the best-fitting Lumi-nosity Dependent Luminosity Evolution(model C in Table2).Error bars as in Fig.2.With this model,in this redshift interval and for mag-nitudes brighter than M B=−25,29QSOs are ex-pected in comparison with the32observed.In this way,as shown in Fig.1,the LDLE repro-duce the higher counts of bright QSOs at B<16.4, discovered by the HBQS and EQS surveys,much better than the PLE models:a surface density of 0.017deg−2is predicted with respect to0.016deg−2 observed.The A model by Boyle(1992)predicts a surface density of0.008deg−2.It is important to notice that both the PLE and the LDLE models do not reproduce a2σsignificant observed underdensity of faint QSOs(−23>M B>−25)in the redshift range0.3<z<0.6.In this bin,with the PLE B model,125QSOs are observed and161expected.It is possible tofind less signifi-cant indications of this feature in the data analyzed by Boyle(1992).We examined the possibility that this observed underdensity of the faint part of the lu-minosity function at low redshift is due to an underes-timated incompleteness of the UVx optical selection method at low redshift.For this reason we have car-ried out simulations assuming a redder U−B QSO color of0.2magnitudes in the interval0.3<z<0.8. The effects were still insufficient to account for the underdensity at low redshift(125QSOs observed and 154expected).As our bestfit probabilities are sat-isfactory,we preferred not to model the low redshift faint feature.It is worth to notice that the determina-tion of the local(z=0)AGN(Seyfert1plus QSOs) LF from the Hamburgh Bright QSO Survey(Wisotzki et al.1996a)shows similar trends,with evidences of higher densities at bright magnitudes and lower densities at faint magnitudes in comparison with the de-evolved PLE LF by Boyle(1992)(Wisotzki et al. 1996b;K¨o hler1996).Adopting a q o=0.1Universe,as shown in Table 2,thefitting of the data with the PLE model(I)by Boyle(1992)is rejected at0.004confidence level.Our PLE model(L)obtains an acceptable global represen-tation of the data(χ2probability0.36),slightly better than the PLEfit in a q o=0.5Universe.However,in the0.3<z<0.6redshift range the PLE still un-derestimates the expected number of QSOs,although the discrepancy is less serious than in the q o=0.5 case:44QSOs with M B<−25are observed versus 33predicted in our L model(24in the I model).The introduction of a LDLE parameterization according to Eq.2provides satisfactory representation of the observations in the low-z domain also for q o=0.1.5.DISCUSSIONWhat is the origin of theflattening of the lumi-nosity function at low-redshift and is it confirmed by observations in other wavebands?In the last years evidence has been produced that optically selected QSOs have a bimodal distribution of radioflux densities,and that the fraction of ra-dio loud QSOs decreases with increasing redshift and decreasing absolute optical luminosity(Miller et al. 1990;Visnovsky et al.1992;Schneider et al.1992; Padovani1993;La Franca et al.1994).La Franca et al.(1994)have determined that the radio-loud fraction is substantially higher for QSOs with z<1,a result essentially due to the higher overall radio-loud fraction in the predominantly low redshift PG sample.The radio-loud fraction has also been found to be larger at bright absolute magni-tudes,regardless of whether or not the PG sample is included in the Franca et al.(1994) have been able to reproduce the data with a radio-loud optical luminosity function(OLF)characterized by a lower space density,a similar shape and a smaller evolutionary parameter k(2.7<k<3.1)with re-spect to the parent total(radio-quiet plus radio-loud) QSO population.According to this picture theflat-tening of the bright part of the OLF corresponds to an increase of the radio-loud OLF contribution.However,the decrement of the radio-loud fraction with redshift relies essentially on the PG sample and has not been confirmed by a study of256QSOs in the LBQS(Hooper et al.1995).Nevertheless there is a very small overlap in the magnitude redshift plane between the LBQS and the PG sample:the LBQS QSOs are too faint and too high-redshift to be com-pared with the PGs.Our observed overdensity of low redshift(0.3<z<0.6)QSOs involves the QSOs with B<16.5and M B<−25but in the LBQS there are only two such QSOs with B<16.5,to be compared with the45QSOs of the PG sample.In the EQS plus HBQS combined sample there are16QSO brighter than16.5.It becomes crucial to obtain radio data of this QSO subsample.Other information on the evolution of the LF and on the dependence of the radio loud fraction on mag-nitude and redshift can be derived from QSO samples selected in the soft X-rays.A study of the EMSS AGN sample by Maccacaro et al.(1991)and Della Ceca et al.(1992)has shown that a PLE model with a power-law dependence on the redshift,L x(z)=L x(0)(1+z)k,provides the sim-plest description of data.Their best-fitting evolution rate(k x=2.56)is almost one unit lower than the optical bestfit.Boyle et al.(1993)used a new sam-ple of faint AGNs selected by ROSAT,combined with the EMSS sample,to derive a value of k=ing the same data Franceschini et al.(1994)showed that the evolution rate of X-ray selected AGNs could have been underestimated and actually be comparable to that of the QSOs in the optical,with a linear scaling of the emission in the two bands.Boyle et al.(1994) using an enlarged sample of107faint AGNs selected by ROSAT,combined with EMSS sample,derived an evolution L x(z)=L x(0)(1+z)3.25at z<1.6,quite similar to that of optically selected QSOs.The lat-ter two analyses favour a picture in which the same QSO population is observed,both in the soft-X and in the optical.If this is true,at low z,bright X-ray selected samples should show aflattening of the。

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2022年考研考博-考博英语-湖南师范大学考试全真模拟易错、难点剖析AB卷(带答案)试题号：74

2022年考研考博-考博英语-湖南师范大学考试全真模拟易错、难点剖析AB卷(带答案)试题号：74

2022年考研考博-考博英语-湖南师范大学考试全真模拟易错、难点剖析AB卷（带答案）一.综合题(共15题)1.单选题Professor Hawking is（）as one of the world’s greatest living physicists.问题1选项A.dignifiedB.clarifiedC.acknowledgedD.illustrated【答案】C【解析】dignify使高贵，授予荣誉；clarify澄清，阐明；acknowledge承认，认可；illustrate阐明，举例。

句意：霍金教授被公认是当今世界上最伟大的物理学家之一。

选项C符合语境。

2.翻译题参与并取胜，这就是奥林匹克精神。

他表现于弱者勇于向强者挑战，也表现于强者力争取得更好的成绩。

胜而又胜，优而更优，这种理想一直鼓舞着运动员奋力前进。

有人说竞技者终宄会是失败者，即使是最佳运动员也终将被更强者淘汰。

成千上万个失败者才涌现一个胜利者，这个胜利者最终仍将被取代，挤出光荣榜——这就是竞技运动的规律。

然而运动员却从不为这种不可避免的失败结局所沮丧，仍然力争最佳发挥。

【答案】To participate and to win—that is the Olympic spirit. It finds expression in the weak daring to defy the strong, and the strong striving for ever better performance. Ever better—the ideal always luring a sportsman forward. It is said that none of the competitors can avoid being defeated—even the best is bound to be surpassed by someone still stronger. Thousands of losers set off one victor who in turn will eventually be replaced by someone on the honor list. This is the rule of sports. However, undaunted by the inevitable failure, he is always striving to do the best he can.3.单选题He gave us an（）consent to take the apples, for he smiled when he saw us do it问题1选项A.exaggeratedB.implicitC.impartialD.extravagant【答案】B【解析】exaggerated夸张的；implicit含蓄的, 暗示的；impartial公正的；extravagant奢侈的, 浪费的。

考研英语-111_真题(含答案与解析)-交互

考研英语-111_真题(含答案与解析)-交互

考研英语-111(总分100, 做题时间90分钟)Section Ⅰ Use of EnglishDirections:Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C, and D on ANSWER SHEET 1.The world religion is derived from the Latin noun religion, which denotes both (1) observance of ritual obligations and an inward spirit of reverence. In modern usage, religion covers a wide spectrum of (2) that reflects the enormous variety of ways the term can be (3) . At one extreme, **mitted believers (4) only their own tradition as a religion, understanding expressions such as worship and prayer to refer (5) to the practices of their tradition. They may (6) use vague or idealizing terms in defining religion, (7) , true love of God, or the path of enlightenment. At the other extreme, religion may be equated with (8) , fanaticism, or wishful thinking.By defining religion as a sacred engagement with what is taken to be a spiritual reality, it is possible to consider the importance of religion in human life without making (9) about what is really is or ought to be. Religion is not an object with a single, fixed meaning, or (10) a zone with clear boundaries. It is an aspect of human (11) that may intersect, incorporate, or transcend other aspects of life and society. Such a definition avoid the drawbacksof (12) the investigation of religion to Western or biblical categories (13) monotheism or church structure, which arenot (14) .Religion in this understanding includes a complex of activities that cannot be (15) to any single aspect of human experience. It is a part of individual life but also of (16) dynamics. Religion includes not only patterns of language and thought. It is sometimes an (17) part of a culture. Religious experience may beexpressed (18) visual symbols, dance and performance, elaborate philosophical systems, legendary and imaginative stories,formal (19) , and detailed rules of some ways. There are as many forms of religious expression as there are human cultural (20) .SSS_SINGLE_SEL1.A earnestB clumsyC naiveD frivolous该题您未回答:х该问题分值: 0.5答案:ASSS_SINGLE_SEL2.A urgencyB meaningC conditionD sense该题您未回答:х该问题分值: 0.5答案:BSSS_SINGLE_SEL3.A exhibitedB translatedC interpretedD illustrated该题您未回答:х该问题分值: 0.5答案:CSSS_SINGLE_SEL4.A assureB admitC indulgeD recognize该题您未回答:х该问题分值: 0.5答案:DSSS_SINGLE_SEL5.A excessivelyB comprehensivelyC flexiblyD exclusively该题您未回答:х该问题分值: 0.5答案:DSSS_SINGLE_SEL6.A neverthelessB moreoverC furthermoreD accordingly该题您未回答:х该问题分值: 0.5答案:ASSS_SINGLE_SEL7.A in a senseB as a resultC for exampleD for all该题您未回答:х该问题分值: 0.5答案:CSSS_SINGLE_SEL8.A ignoranceB awarenessC aversionD insistence该题您未回答:х该问题分值: 0.5答案:ASSS_SINGLE_SEL9.A wishesB claimsC attemptsD pleas该题您未回答:х该问题分值: 0.5答案:BSSS_SINGLE_SEL10.A barelyB hardlyC everD even该题您未回答:х该问题分值: 0.5答案:DSSS_SINGLE_SEL11.A institutionB attributeC distinctionD experience该题您未回答:х该问题分值: 0.5答案:DSSS_SINGLE_SEL12.A limitingB fasteningC tighteningD fixing该题您未回答:х该问题分值: 0.5答案:BSSS_SINGLE_SEL13.A such asB for instanceC in particularD as to该题您未回答:х该问题分值: 0.5答案:ASSS_SINGLE_SEL14.A permanentB apparentC universalD exceptional该题您未回答:х该问题分值: 0.5答案:CSSS_SINGLE_SEL15.A imitatedB houndC reducedD exposed该题您未回答:х该问题分值: 0.5答案:CSSS_SINGLE_SEL16.A strandB groupC classD band该题您未回答:х该问题分值: 0.5答案:BSSS_SINGLE_SEL17.A dominantB principalC prevalentD integral该题您未回答:х该问题分值: 0.5答案:DSSS_SINGLE_SEL18.A in line withB in terms ofC in regard toD in exchange for该题您未回答:х该问题分值: 0.5答案:BSSS_SINGLE_SEL19.A ceremoniesB occasionsC associationsD formalities该题您未回答:х该问题分值: 0.5答案:ASSS_SINGLE_SEL20.A outlooksB circumstancesC environmentsD surroundings该题您未回答:х该问题分值: 0.5答案:CSection Ⅱ Reading ComprehensionPart ADirections:Reading the following four texts. Answer the questions below eachtext by choosing A, B, C or D. Mark your answers on ANSWER SHEET 1. Text 1The discovery of life beyond Earth would transform not only our science but also our religions, our belief systems and our entire world-view. For in a sense, the search for extraterrestrial life is really a search for ourselves--who we are and what our place is in the grand sweep of the cosmos.Contrary to popular belief, speculation that we are not alone in the universe is as old as philosophy itself. The essential steps in the reasoning were based on the atomic theory of the ancient Greek philosopher Democritus. Yet philosophy is one thing, filling in the physical details is another. Although astronomers increasingly suspect that biofriendly planets may be abundant in the universe, the chemical steps leading to life remain largely mysterious.Traditionally, biologists believed that life is a freak--the result of a zillion-to-one accidental concatenation of molecules. It follows that the likelihood of its happening again elsewhere in the cosmos is infinitesimal. This viewpoint derives from the second law of thermodynamics, which predicts that the universe is dying--slowly and inexorably degenerating toward a state of total chaos. Andsimilar reasoning applies to evolution. According to the orthodox view, Darwinian selection is utterly blind. Any impression that the transition from microbes to man represents progress is pure chauvinism of our part. The path of evolution is merely a random walk through the realm of possibilities.If this is right, there can be no directionality, no innate drive forward; in particular, no push toward consciousness and intelligence. Should Earth be struck by an asteroid, destroying all higher life-forms, intelligent beings would almost certainly not arise next time around. There is, however, a contrary view--one that is gaining strength and directly challenges orthodox biology. It is **plexity can emerge spontaneously through a process of self- organization. If matter and energy have an inbuilt tendency to amplify and channel **plexity, the odds against the formation of life and the subsequent evolution of intelligence could be drasticallyshortened.Historically, Bertrand Russell argued that a universe under a death sentence from the second law of thermodynamics rendered human life ultimately futile. All our achievements, all our struggles, "all the noonday brightness of human genius," as he put it, would, in the final analysis, count for nothing if the very cosmos itself is doomed. But what if, in spite of the second law of thermodynamics, there can be systematic progress alongside decay? For those who hope for a deeper meaning or purpose beneath physical existence, the presence of extraterrestrial life-forms would provide a spectacular boost, implying that we live in a universe that is in some sense getting better and better rather than worse and worse.SSS_SINGLE_SEL21.The writer organizes his ideas in the text mainly byA justifying popular beliefs.B **parisons.C looking back on history.D posing sharp contrasts.该题您未回答:х该问题分值: 2答案:DSSS_SINGLE_SEL22.On the possibilities of life beyond Earth astronomers' and ancient philosophers' views areA opposite.B similar.C divergent.D contrary.该题您未回答:х该问题分值: 2答案:BSSS_SINGLE_SEL23.It is the belief of orthodox biology that Darwinian evolutionismA is fully based on illusions.B focuses purely on reasoning.C is utterly entitled to worship.D comes to account for nothing.该题您未回答:х该问题分值: 2答案:ASSS_SINGLE_SEL24.Under the law of thermodynamics, the universe is supposedA to push forward progress.B to give rise to other life forms.C to make for a total chaos.D to improve by wide margins.该题您未回答:х该问题分值: 2答案:CSSS_SINGLE_SEL25.If there were push to direct **plexity, chances of intelligence evolution wouldA be wrecked.B level off.C be shortened.D crop up.该题您未回答:х该问题分值: 2答案:DText 2"My own feelings went from disbelief to excitement to downright fear," says Carl Hergenrother, 23, an Arizona undergraduate who verified a large asteroid barreling toward Earth with a 230cm telescope atop nearby Kitt Peak. "It was scary, because there was the possibility that we were confirming the demise of some city somewhere, or some state or small country."Well, not quite. Early last week, his celestial interloper whizzed by Earth, missing the planet by 450620 km--a hairbreadth in astronomical terms. Perhaps half a kilometer across, it was the largest object ever observed to pass that close to Earth.Duncan Steel, an Australian astronomer, has calculated that if the asteroid had struck Earth, it would have hit at some 93460 km/h. The resulting explosion, scientists estimate, would have been in the 3000-to-12000-megaton range. That, says astronomer Eugene Shoemaker, a pioneer asteroid **et hunter, "is like taking all of the U. S. and Soviet nuclear weapons, putting them in one pile and blowing them all up."And what if one them is found to be on a collision course with Earth? Scientists at the national laboratories at Livermore, California, and Los Alamos, New Mexico, have devised a number of ingenious plans that, given enough warning time, could protect Earth from a threatening NEO. Their defensive weapons of choice includelong distance missiles with conventional or, more likely, nuclear warheads that could be used either to nudge an asteroid into a safe orbit or blast it to smithereens.Many people including some astronomers--are understandably nervous about putting a standby squadron of nuclear tipped missiles in place. Hence the latest strategy, which in some cases would obviate the need for a nuclear defense: propelling a fusillade of cannonball-size steel spheres at an approaching asteroid. In a high-velocity encounter with a speeding NEO, explains Gregory Canavan, a senior scientist at Los Alamos, "the kinetic energy of the balls, would change into heat energy and blow the thing apart."Some astronomers oppose any immediate defensive preparations, citing the high costs and low odds of a large object's striking Earth in **ing decades. But at the very least, Shoemaker contends, NEO detection should be accelerated. "There's this thing called the'giggle factor' in Congress," he says. "people in Congress and also at the top level in NASA still don't take it seriously. But we should move ahead. It's a matter of prudence."The world, however, still seems largely unconcerned with the danger posed by large bodies hurtling in from space, despite the spectacle two years ago of Comet Shoemaker-Levy 9 riddling the planet Jupiter with mammoth explosions. It remains to be seen whether last week's record near-miss has changed any minds.SSS_SINGLE_SEL26.From the first three paragraphs, we learn thatA the earth narrowly escaped a catastrophe.B one asteroid almost destroyed an entire city.C asteroids **parable to nuclear weapons.D the planet earth is vulnerable to dangers.该题您未回答:х该问题分值: 2答案:ASSS_SINGLE_SEL27.When mentioning the "the 3000-to-12000-megaton range" (Para. 3), the writer is talking aboutA striking spectacles.B conventional weapons.C explosive impact.D defensive strategies.该题您未回答:х该问题分值: 2答案:CSSS_SINGLE_SEL28.The description of Congress's "giggle factor" (Para. 6) shows the writer'sA appreciation.B disbelief.C excitement.D ridicule.该题您未回答:х该问题分值: 2答案:DSSS_SINGLE_SEL29.According to the text, "nuclear tipped missiles" and "cannonball-size steel spheres" (Para. 5)A are different in nature.B serve similar functions.C are identical to each other.D pose real challenges.该题您未回答:х该问题分值: 2答案:BSSS_SINGLE_SEL30.It seems that the writer isA active to fend off invading asteroids.B largely unconcerned with the danger.C interested in military initiatives.D enthusiastic about spotting asteroids.该题您未回答:х该问题分值: 2答案:AText 3AMERICA'S central bank sent a clear message this week. For the second consecutive meeting, the Federal Open Market Committee, the central bank's policy-**mittee, left short term interest rates unchanged at 1.75%. But it said that the risks facing the economy had shifted from economic weakness to a balance between weakness and excessive growth. This shift surprised no one. But it has convinced many people that interest rates are set to rise again--and soon.Judging by prices in futures markets, investors are betting that short-term interest rates could start rising as early as May, andwill be 1.25 percentage points higher by the end of the year. Thatmay be excessive. Economists at Goldman Sachs, who long argued that the central bank would do nothing this year, now expect short-term rates to go up only 0.75% this year, starting in June. But virtually everyone reckons some Fed tightening is in the offing.The reason? After an unprecedented 11 rate-cuts in 2001, short term interest rates are abnormally low. As the signs of robust recovery multiply, analysts expect the Fed to take back some of the rate-cuts it used as an "insurance policy" after the September 11th terrorist attack. They think there will be a gradual move from the Fed's current "accommodative" monetary stance to a more neutral policy. And a neutral policy, many argue, ultimately implies short term interest rates of around 4 %.Logical enough. But higher rates could still be further off, particularly if the recovery proves less robust than many hope. Certainly, recent economic indicators have been extraordinarily strong: unemployment fell for the second consecutive month in February and industrial production rose in both January and February. The manufacturing sector is growing after 18 months of decline. The most optimistic Wall Streeters now expect GDP to have expanded by between 5% and 6% on an annual basis in the first quarter.But one strong quarter does not imply a sustainable recovery. In the short term, the bounce-back is being driven by a dramatic restocking of inventories. But it can be sustained only if corporate investment recovers and consumer spending stays buoyant. With plenty of slack capacity around and many firms stuck with huge debts and lousy profits, it is hard to see where surging investment **e from. And, despite falling unemployment, America's consumers could disappoint the bulls.These uncertainties alone suggest the central bank will be cautious about raising interest rates. Indeed, given the huge pressure on corporate profits, the Federal Reserve might be happy to see consumer prices rise slightly. In short, while Wall Street frets about when and how much interest rates will go up. The answer may well be not soon and not much.SSS_SINGLE_SEL31.The purpose of the author in writing this text is toA interpret the message from the central bank,B justify the rise of short term interest rates.C illustrate what is weakness and undue growth.D contrast different views on economic indices.该题您未回答:х该问题分值: 2SSS_SINGLE_SEL32.How does everyone feel about the message given by America's central bank?A Encouraged.B Panicked.C Confused.D Misguided.该题您未回答:х该问题分值: 2答案:CSSS_SINGLE_SEL33.The phrase "current 'accommodative' monetary stance" (Para. 3) denotesA "optimal."B "excessive."C "logical."D "prudent."该题您未回答:х该问题分值: 2答案:DSSS_SINGLE_SEL34.Despite signs Of strong economic recovery, **panies are still pressed forA tremendous debts.B considerable profits.C soaring investment.D excessive growth.该题您未回答:х该问题分值: 2答案:BSSS_SINGLE_SEL35.Which of the following is true according to this text?A Short-term interest rates should be guarded wisely.B Unemployment no longer constitutes a problem.C A sustainable recovery depends on corporate profits.D Too much caution might suspend economic growth.该题您未回答:х该问题分值: 2Text 4Come on, my fellow white folks, we have something to confess. Out with it, friends, the biggest secret known to whites since the invention of powdered rouge: welfare is a white program. The numbers go like this: 61% of the population receiving welfare, listed as "means-tested cash assistance" by the Census Bureau, is identified as whit e, while only 33% is identified as black. These numbers notwithstanding, the Republican version of "political correctness" has given us "welfare cheat" as a new term for African American since the early days of Ronald Reagan.Our confession surely stands: white folks have been gobbling up the welfare budget while blaming someone else. But it's worse than that. If we look at Social Security, which is another form of welfare, although it is often mistaken for an individual insurance program, then whites are the ones who are crowding the trough. We receive almost twice as much per capita, for an aggregate advantage to our race of ＄10 billion a year--much more than the ＄ 3. 9billion advantage African American gain from their disproportionate share of welfare. One sad reason: whites live an average of six years longer than African Americans, meaning that young black workers help subsidize a huge and growing "over-class" of white retirees. I do not see our confession bringing much relief. There's a reason for resentment, though it has more to do with class than with race. White people are poor too, and in numbers far exceeding any of our more generously pigmented social groups. And poverty as defined by the government is a vast underestimation of the economic terror that persists at incomes--such as ＄ 20,000 or even ＄ 40,000 and above--that we like to think of as middle class.The problem is not that welfare is too generous to blacks but that social welfare in general is too stingy to all concerned. Naturally, whites in the swelling "near poor" category resent the notion of whole races supposedly frolicking at their expense. Whites, near poor and middle class, need help too--as do the many African Americans.So we white folks have a choice. We can keep pretending that welfare is black program and a scheme for transferring our earnings to the pockets of shiftless, dark-skinned people. Or we can clear our throats, blush prettily and admit that we are hurting too--for cash assistance when we're down and out, for health insurance, for college aid and all the rest. Racial scapegoating has its charms, I will admit: the surge of righteous anger, even the fun--for thoseinclined--of wearing sheets and burning crosses. But there arebetter, nobler sources of white pride, it seems to me. Remember this: only we can truly, deeply blush.SSS_SINGLE_SEL36.White folks in U. S. are at a greater advantage in thatA they obtain more benefits from welfare.B they show contempt for African Americans.C they blame the blacks for welfare theft.D they have a choice to their best interests.该题您未回答:х该问题分值: 2答案:ASSS_SINGLE_SEL37.It can inferred from the 2nd paragraph thatA black workers are generous unless wrongly accused.B whites have a longer life expectancy than blacks.C black people may contribute much to welfare budgets.D whites receive less financial aid than blacks.该题您未回答:х该问题分值: 2答案:CSSS_SINGLE_SEL38.The expression "racial scapegoating" (Para. 4) best denotesA anger at the mercy of laws.B an aid in terms of prejudice.C relief for the sake of classes.D a victim in the name of races.该题您未回答:х该问题分值: 2答案:DSSS_SINGLE_SEL39.The author is most critical of the whites'A confession.B hypocrisy.C arrogance.D hysteria.该题您未回答:х该问题分值: 2答案:BSSS_SINGLE_SEL40.The function of the last paragraph isA to reverse the previously expressed thoughts.B to advance the final argument.C to heap praises upon the pride of the whites.D to echo the thesis statement.该题您未回答:х该问题分值: 2答案:DPart BDirections:You are going to read a list of headings and a text about happiness. Choose the most suitable heading from the list A--F for each numbered paragraph (41- 45). The first and last paragraphs of the text are not numbered. There is one extra heading which you do not need to use. Mark your answers on ANSWER SHEET 1.[A] Various definitions and interpretations of happiness.[B] One episode of enjoying happiness.[C] Some misconceptions about happiness.[D] Where to seek happiness?[E] Happiness is equivalent to the ability to rejoice.[F] **plexity of how to define happiness."Are you happy?" I asked my brother, Ian, one day. "Yes. Nod It depends what you mean," he said."Then tell me," I said, "when was the last time you think you were happy?""April 1967," he said.It served me right for putting a serious question to someone who has joked his way through life. But Ian's answer reminded me that when we think about happiness, we usually think of something extraordinary, a pinnacle of sheer delight--and those pinnacles seem to get rarer the older we get.41．________________________.For a child, happiness has a magical quality. I remember making hide-outs in newly cut hay, playing cops and robbers in the woods, getting a speaking part in the school play. Of course, kids also experience lows, but their delight at such peaks of pleasure as winning a race or getting a new bike is unreserved. In the teenage years the concept of happiness changes. Suddenly it's conditional on such things as excitement, love, popularity and whether that zit will clear up before prom night I can still feel the agony of not being invited to a party that almost everyone else was going to. But I also recall the ecstasy of being plucked from obscurity at another eventto dance with a John Travolta look-alike. In adulthood the thingsthat bring profound joy--birth, love, marriage--also bring responsibility and the risk of loss. Love may not last, sex isn't always good, loved ones die. For adults, happiness is complicated.42．________________________.My dictionary defines happy as "lucky" or "fortunate," but I think a better definition of happiness is "the capacity for enjoyment." The more we can enjoy what we have, the happier we are.It's easy to overlook the pleasure we get from loving and being loved, **pany of friends, the freedom to live where we please, even good health. I added up my little moments of pleasure yesterday.First there was sheer bliss when I shut the last lunchbox and had the house to myself. Then I spent an uninterrupted morning writing, which I love. When the kids came home, I enjoyed their noise after the quiet of the day. Later, peace descended again, and my husband and I enjoyed another pleasure-intimacy. Sometimes just the knowledge that he wants me can bring me joy. 43．________________________.You never know where happiness will turn up next. When I asked friends what makes them happy, some mentioned seemingly insignificant moments. "I hate shopping," one friend said. "But there's this clerk who always chats and really cheers me up." Another friend loves the telephone. "Every time it rings, I know someone is thinking about me."44．________________________.I get a thrill from driving. One day I stopped to let a school bus turn onto a side road. The driver grinned and gave me a thumbs-up sign. We were two allies in a world of mad motorists. It made me smile. We all experience moments like these. Too few of us register then as happiness.45．________________________.Psychologists tell us that to be happy we need a blend of enjoyable leisure time and satisfying work. I doubt that my great-grandmother, who raised 14 children and took in washing, had much of either. She did have a net-work of close friends and family, and maybe this is what fulfilled her. If she was happy with what she had, perhaps it was because she didn't expect life to be very different. We, on the other hand, with so many choices and such pressure to succeed in every area, have turned happiness into one more thing we "gotta have." We're so self-conscious about our "right" to it thatit's making us miserable. So we chase it and equate it with wealth and success, without noticing that the people who have those things aren't neeessaiily happier.While happiness may be **plex for us, the solution is the sameas ever. Happiness isn't about what happens to us--it's about how we perceive what happens to us. It's the knack of finding a positive for every negative, and viewing a setback as a challenge. It's not wishing for what we don't have, but enjoying what we do possess.SSS_FILL41.该题您未回答:х该问题分值: 2答案:ASSS_FILL42.该题您未回答:х该问题分值: 2答案:ESSS_FILL43.该题您未回答:х该问题分值: 2答案:DSSS_FILL44.该题您未回答:х该问题分值: 2答案:BSSS_FILL45.该题您未回答:х该问题分值: 2答案:CPart CDirections:Read the following text Carefully and then translate the underlinedsegments into Chinese. Your translation should be written clearly on ANSWER SHEET 2.The level of economic and industrial development enjoyed by a state affects the foreign policy goals it can pursue. (46) As a general proposition, the more developed a state is economically, the more likely it is that it will play an activist role in the world political economy. Rich nations have interests that extend far beyond their borders and **mand the means necessary to pursue and protect them. (47) Not coincidentally, countries that enjoy industrial capabilities and extensive involvement in international trade also tend to be militarily powerful, in part because military might is a function of economic capabilities. For two decades after world war two, the United States and the Soviet Union stood out as superpowers precisely because they benefited from **bination of economic and military capability including extensive arsenals of nuclear weapons and the means to deliver them anywhere, that enabled both to practice unrestrained globalism. Their imperial reach and interventionist behaviors were seemingly unrestrained by limited wealth or resources. In fact, major powers have been involved in foreign conflict more frequently than minor powers.Although economically advanced nations are more active globally, this does not mean that their privileged circumstances dictate adventuresome policies. Rich nations are usually " satisfied" ones that have much to lose from the onset of revolutionary change or global instability. (48) For this reason, they usually perceive preservation of the status quo as serving their interests best, and they often practice international economic policies designed to protect and expand their envied position at the pinnacle of the global hierarchy.Levels of productivity and prosperity also affect the foreign policies of the poor states at the bottom of the hierarchy. (49) Some respond to their economic weakness by complying subserviently with the wishes of the rich on which they depend. Others rebel defiantly, and they sometimes succeed in resisting major power efforts tocontrol their international behavior.Hence efforts to generalize about the economic foundations of states' international political behavior often prove unrewarding. Levels of economic development vary widely among states in the international system, but they do not by themselves determine foreign policies. (50) Instead the opportunities and constraints that leaders perceive in their nation's attributes, rather than the actual level of development, may be the determining source of states'international conduct.SSS_TEXT_QUSTI。

2022年考研考博-考博英语-中国海洋大学考试预测题精选专练VII(附带答案)卷20

2022年考研考博-考博英语-中国海洋大学考试预测题精选专练VII(附带答案)卷20

2022年考研考博-考博英语-中国海洋大学考试预测题精选专练VII（附带答案）第1套一.综合题(共25题)1.单选题Successful innovations have driven many older technologies to extinction and have resulted in higher productivity, greater consumption materials through the economy and increased quantities of metals and other substances in use per capita. The history of industrial development abounds with examples.In 1870, horses and mules were the prime source of power on US farms. One horse or mule was required to support four human beings — a ration that remained almost constant for many decades. At that time, had a national commission been asked to forecast the horse and mule population for 1970, its answer probably would have depended on whether its consultants were of an economic or technological turn of mind. Had they been “economists”, they would probably have projected the 1970 horse or mule population to be more than 50 million. Had they been “technologists”，they would have recognized that the power of steam had already been harnessed to industry and to land and ocean transport. They would have recognized further that it would be only a matter of time before steam would be the prime source of power on the farm. It would have been difficult for them to avoid the conclusion that the horse and mule population would decline rapidly.1.According to the passage, what supplied most of the power on U.S. farms in 1870?2.Which of the following is NOT mentioned by the author as a consequence of new technological developments?3.It can be inferred from the passage that by 1870（）.4.In the second paragraph, the author suggests that “economists” would（）.问题1选项A.AnimalsB.HumansC.EnginesD.Water问题2选项A.Older technologies die away.B.The quality of life is improved.C.Overall productivity increasedD.More raw materials become necessary问题3选项A.technology began to be more commercialB.the steam engine had been inventedC.the U.S. horse population was about 10 millionD.a national commission on agriculture had been established问题4选项A.plan the economy through yearly forecastsB.fail to consider the influence of technological innovationD.consult for the national commission on the economy问题5选项A.He is excited about themB.He accepts them as naturalC.He is disturbed by themD.He questions their usefulness【答案】第1题:A第2题:B第3题:B第4题:B第5题:B【解析】1.细节事实题。

2022年考研考博-考博英语-浙江工商大学考试全真模拟全知识点汇编押题第五期(含答案)试卷号：42

2022年考研考博-考博英语-浙江工商大学考试全真模拟全知识点汇编押题第五期(含答案)试卷号：42

2022年考研考博-考博英语-浙江工商大学考试全真模拟全知识点汇编押题第五期（含答案）一.综合题(共15题)1.单选题Some studies confirmed that this kind of eye disease was （）in tropical countries.问题1选项A.prospectiveB.prevalentC.provocativeD.perpetual【答案】B【解析】【试题解析】考查形容词辨析。

A选项prospective“未来的、预期的”；B选项prevalent“流行的、普遍的”；C选项provocative“刺激的、挑拨的”；D选项perpetual“永久的、永远的”，从句中关键词“eye disease眼疾，tropical countries热带国家”可联系到prevalent“流行的、普遍的”。

句意为：一些研究证实这种眼疾在热带国家很普遍。

故正确答案选B。

2.单选题Not until they climbed to the top of the hill （）what they had been told.问题1选项A.that they believedB.did they believeC.when they believedD.then they believed【答案】B【解析】【试题解析】考查语法结构。

这里考查的是部分倒装结构。

not until位于句首时，句子要倒装。

not until +从句，助动词+主语+谓语动词原形+剩余成分；空格部分所在的句子中，需要将did助动词提前，句意为：直到他们爬上山顶，他们才相信别人所说的。

故正确答案选B。

3.单选题（） is his own decision.问题1选项A.When leavingB.When does he leaveC.When he leavesD.He leaves【答案】C【解析】【试题解析】考查语法结构。