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2022年考研考博-考博英语-西北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Psychologists think of attitudes as being predisposition toward objects or events that determine the way people react to different stimuli.问题1选项A.prior inclinationsB.prescriptionsC.precautionsD.principal commitments【答案】A【解析】心理学家认为态度是对事物或事件的一种倾向，它决定了人们对不同刺激的反应方式。
predisposition意为“ 倾向”。
prior inclinations 倾向，爱好；prescriptions 医药处方；precautions预防措施，预警；principal commitments主要承诺。
选项A与之意思相近。
2.单选题The use of robots and automated machinery has eliminated certain （）factory jobs.问题1选项A.thrillingB.timidC.enticingD.tedious【答案】D【解析】thrilling 激动人心的；令人兴奋的；timid 胆小的，羞怯的；enticing 有吸引力的，诱人的；tedious 沉闷的，冗长乏味的。
句意：机器人和自动化机器的使用消除了某些单调乏味的工厂工作。
选项D符合句意。
3.翻译题大学之所以有理由存在，是因为它使老少两代人在富于想象力的学习中，保持了知识与生活热情之间的联系。
大学提供信息，但它是富于想象地提供信息。
至少，这是它应该为社会发挥的作用。
一所大学如果做不到这一点，就没有理由存在。
富于想象的思维可以营造出一种令人兴奋的氛围，而这种氛围又可以转化知识。
IntroductionThe concept of a pre-emptive strategy is deeply rooted in the realms of military tactics, business strategies, and international relations, often serving as a proactive measure to mitigate potential threats or exploit emerging opportunities. This approach involves taking decisive action before an adversary can do so, thereby gaining a strategic advantage. The application of this principle across various domains necessitates a thorough understanding of its dynamics and implications from multiple perspectives, especially when aiming for high-quality and high-standard decision-making.1. **Military Dimension**In the context of military strategy, a pre-emptive strike is a calculated offensive action undertaken to defeat an enemy's ability or intention to attack. This approach was notably employed in historical events such as the Six-Day War by Israel in 1967. From a high-quality, high-standard perspective, a successful pre-emptive military strategy requires meticulous intelligence gathering, advanced logistical planning, and precision execution. It must be backed by clear evidence of an imminent threat and align with ethical and legal frameworks to ensure it doesn't undermine global peace and stability.2. **Business and Economic Perspective**In the corporate world, a pre-emptive strategy might involve launching a new product, acquiring a competitor, or investing in innovative technology before rivals can. For instance, tech giants like Apple have often adopted a pre-emptive approach by continuously innovating and introducing products that disrupt markets before competitors can catch up. To execute such strategies at a high standard, businesses need to possess strong foresight, agile innovation capabilities, robust risk assessment, and a deep understanding of market dynamics. Quality here is measured by the effectiveness of the strategy in securing long-term competitive advantages and sustainable growth.3. **International Relations and Diplomacy**In international diplomacy, a pre-emptive strategy could mean diplomaticinitiatives to prevent conflicts, economic sanctions to deter aggressive behavior, or early negotiations to resolve disputes. The high standards lie in the ability to predict and defuse crises while maintaining respect for international law and norms. Quality in this realm means crafting smart policies that balance assertiveness with cooperation, promoting stability and mutual benefits over unilateral gains.4. **Environmental and Health Policy**Pre-emptive strategies also play a significant role in public health and environmental policy. Anticipatory measures such as vaccination campaigns before an epidemic spreads or preventative pollution control measures demonstrate this approach. Here, high quality and standards require scientific accuracy, swift response mechanisms, and equitable distribution of resources to protect the most vulnerable populations.5. **Legal and Regulatory Frameworks**In the legal field, pre-emptive legislation can anticipate future issues and set regulatory standards to prevent harm. For example, data privacy laws often pre-emptively address potential misuse of personal information. The challenge lies in striking the right balance between over-regulation and under-preparation, ensuring that the law is forward-thinking yet practical, and protective without stifling innovation – all hallmarks of a high-quality, high-standard legal framework.ConclusionIn summary, the adoption and execution of a pre-emptive strategy across different sectors require rigorous analysis, careful planning, and bold action. Its success is predicated on the ability to identify key indicators, forecast outcomes accurately, and act decisively within the confines of ethical, legal, and social norms. By adhering to these principles, organizations and governments can harness the power of a pre-emptive strategy to achieve high-quality and high-standard outcomes, whether it’s protecting national security, gaining market share, preserving global stability, safeguarding public health, orshaping regulatory landscapes. However, the complexity and unpredictability of human systems mean that even the best-laid plans may encounter unforeseen challenges; thus, continuous review, adaptation, and learning are crucial components of any effective pre-emptive strategy.While this overview has touched upon several dimensions, each context brings unique nuances that demand tailored approaches to meet the stringent criteria of high-quality, high-standard pre-emption. In essence, pre-emption is not merely about being first; it's about being right, responsible, and responsive in the face of uncertainty.。
九年级英语政治单选题60题1.Which international organization is dedicated to promoting world peace and security?A.UNESCOB.WHOC.UND.WTO答案：C。
本题考查国际组织的职能。
UN（联合国）致力于促进世界和平与安全。
UNESCO 联合国教科文组织）主要致力于教育、科学和文化领域。
WHO（ 世界卫生组织）专注于全球卫生事务。
WTO 世界贸易组织）主要处理国际贸易问题。
2.The Belt and Road Initiative is a major example of ________.A.international cooperationB.domestic developmentC.regional conflictD.global isolation答案：A。
“一带一路”倡议是国际合作的重要范例。
B 选项国内发展不准确。
C 选项区域冲突与“一带一路”相悖。
D 选项全球孤立也不符合“一带一路”的理念。
3.Which of the following is NOT an international organization involved in economic cooperation?A.APECB.NATOC.OECDD.G20答案：B。
NATO（ 北大西洋公约组织）主要是军事联盟，不是经济合作组织。
APEC（ 亚太经合组织）、OECD（ 经济合作与发展组织）、G20 二十国集团）都涉及经济合作。
4.The purpose of the World Trade Organization is to ________.A.regulate international tradeB.provide medical assistanceC.promote cultural exchangesD.ensure national security答案：A。
2009年江苏专转本（英语）真题试卷(题后含答案及解析)题型有：1. 2. V ocabulary and Structure 3. Cloze 4. 5. 6. WritingYoung Koreans are beginning to do it alone when it comes to finding a partner, though matchmaking is still the most common way for boys to meet girls. Professional matchmakers can make thousands of American dollars by introducing suitable marriage partners to each other, but partners also play a role in the process during which young Koreans meet. In Confucius Korea, when marriage is regarded as more of a business contract than a sacred thing, the scene of the first meeting is repeated hundreds of times a day in coffee shops in the main hotels around Seoul. The business of continuing the family lineage (血统) and keeping the bloodlines pure is often too important to be left to romance and chance encounters. Often, the girl will work out a system of secret signals with her mother, from which her parents ca. . tell if she is interested. For example, if the girl orders a coffee it might mean that she wants her parents to leave her alone with the boy, while a milk shows that she wants them to stay. Sometimes the matchmaking is not always so formal, with the introduction being made by friends. But whether through friends or families, there is hardly a Korean man or woman in the country who has not gone through this process—sometimes six or seven times.1．The word “matchmaking” in this passage means______.A．a very formal ritual(仪式)attended by boys and girlsB．introducing boys and girls to know each other for the purpose of marriage C．producing matches to make a fire or light a cigaretteD．arranging games between men and women正确答案：B解析：根据文章第二段可知matchmaker(媒人)赚钱的方式是“为别人介绍合适的结婚伴侣”，故matchmaking意思为“做媒”。
高二英语国际关系单选题40题1. The United States once imposed a series of economic sanctions on Iran mainly because of _______ issues.A. nuclearB. environmentalC. culturalD. educational答案：A。
解析：美国对伊朗实施经济制裁主要是围绕核问题。
nuclear表示核的，伊朗核问题是国际关系中的一个重要外交事件相关点。
而environmental是环境的，cultural是文化的，educational是教育的，这几个选项与美国对伊朗制裁的主要原因不符。
2. China's Belt and Road Initiative aims to promote economic cooperation and cultural exchanges among countries along the routes. One of the important aspects is infrastructure building. Which of the following is a typical infrastructure project?A. Building a hospitalB. Constructing a high - speed railwayC. Establishing a universityD. Opening a shopping mall答案：B。
解析：中国一带一路倡议旨在促进沿线国家的经济合作和文化交流，其中基础设施建设是重要方面。
constructing a high - speed railway（修建高速铁路）属于基础设施建设。
Building a hospital更多是医疗卫生方面，establishing a university是教育方面，opening a shopping mall是商业方面，均不符合基础设施建设这个典型的一带一路倡议中的重要内容。
九年级英语政治单选题60题1. There ____ a lot of students in the playground.A. isB. areC. haveD. has答案：B。
本题考查there be 句型的用法。
there be 句型表示“有”，be 动词的形式要根据后面的主语来确定。
students 是复数名词，所以要用are，A 选项is 用于单数名词，C 选项have 和 D 选项has 表示“拥有”，主语通常是人。
2. He often ____ his homework at home.A. forgetsB. forgetC. leftD. leaves答案：D。
本题考查动词的用法。
forget 表示“忘记”，通常忘记某事或某物，leave 有“遗留，落下”的意思。
often 表明是一般现在时，主语he 是第三人称单数，所以动词要用第三人称单数形式，A 选项forgets 不符合语境，C 选项left 是leave 的过去式，所以要用leaves。
3. The teacher asked us ____ quiet in the library.A. to keepB. keepingC. keepD. kept答案：A。
本题考查ask sb. to do sth.的用法，“要求某人做某事”，要用动词不定式，B 选项keeping 是动名词形式，C 选项keep 是动词原形，D 选项kept 是过去式，所以要用to keep。
4. I'm very hungry. I haven't eaten ____ for two days.A. somethingB. anythingC. nothingD. everything答案：B。
本题考查不定代词的用法。
something 通常用于肯定句，anything 用于否定句和疑问句，nothing 表示“没有东西”，everything 表示“一切”。
2023年考研英语一真题及答案详细解析2023年全国硕士硕士入学统一考试英语（一）试题及答案详细解析Section I Use of English :Directions: Read the following text. Choose the best word(s) for each numbered blank and mark A, B,C or D on the ANSWER SHEET. (10 points)Though not biologically related, friends are as “related” as fourth cousins, sharing about 1% of genes. That is _(1)_a study, published from the University of California and Yale University in the Proceedings of the National Academy of Sciences, has__(2)_.The study is a genome-wide analysis conducted _(3)__1,932 unique subjects which __(4)__pairs of unrelated friends and unrelated strangers. The same people were used in both_(5)_.While 1% may seem_(6)_,it is not so to a geneticist. As James Fowler, professor of medical genetics at UC San Diego, says, “Most people do not even _(7)_their fourth cousins but somehow manage to select as friends the people who_(8)_our kin.”The study_(9)_found that the genes for smell were something shared in friends but not genes for immunity .Why this similarity exists in smell genes is difficult to explain, for now,_(10)_,as the team suggests, it draws us to similar environments but there is more_(11)_it. There could be many mechanisms working together that _(12)_us in choosing genetically similar frien ds_(13)_”functional Kinship” of being friends with_(14)_!One of the remarkable findings of the study was the similar genes seem to beevolution_(15)_than other genes Studying this could help_(16)_why human evolution picked pace in the last 30,000 years, with social environment being a major_(17)_factor.The findings do not simply explain people’s_(18)_to befriend those of similar_(19)_backgrounds, say the researchers. Though all the subjects were drawn from a population of European extraction, care was taken to_(20)_that all subjects, friends and strangers, were taken from the same population.1. [A] when [B] why [C] how [D] what2. [A] defended [B] concluded [C] withdrawn [D] advised3. [A] for [B] with [C] on [D] by4. [A] compared [B] sought [C] separated [D] connected5. [A] tests [B] objects [C]samples [D] examples6. [A] insignificant [B] unexpected [C]unbelievable [D] incredible7. [A] visit [B] miss [C] seek [D] know8. [A] resemble [B] influence [C] favor [D] surpass9. [A] again [B] also [C] instead [D] thus10. [A] Meanwhile [B] Furthermore [C] Likewise [D] Perhaps11. [A] about [B] to [C]from [D]like12. [A] drive [B] observe [C] confuse [D]limit13. [A] according to [B] rather than [C] regardless of [D] along with14. [A] chances [B]responses [C]missions [D]benefits15. [A] later [B]slower [C] faster [D] earlier16. [A]forecast [B]remember [C]understand [D]express17. [A] unpredictable [B]contributory [C] controllable [D] disruptive18. [A] endeavor [B]decision [C]arrangement [D] tendency19. [A] political [B] religious [C] ethnic [D] economic20. [A] see [B] show [C] prove [D] tellSection II Reading ComprehensionPart ADirections:Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on ANSWER SHEET. (40 points)Text 1King Juan Carlos of Spain once insisted “kings don’t abdicate, they dare in their sleep.” But embarrassing scandals and the popularity of the republican left in the recent Euro-elections have forced him to eat his words and stand down. So, does the Spanish crisis suggest that monarchy is seeing its last days? Does that mean the writing is on the wall for all European royals, with their magnificent uniforms and majestic lifestyle?The Spanish case provides arguments both for and against monarchy. When public opinion is particularly polarised, as it was following the end of the Franco regime, monarchs canrise above “mere” politics and “embody” a spirit of national unity.It is this apparent transcendence of politics that explains monarchs’ continuing popularity polarized. And also, the Middle East excepted, Europe is the most monarch-infested region in the world, with 10 kingdoms (not counting Vatican City and Andorra). But unlike their absolutist counterparts in the Gulf and Asia, most royal families have survived because they allow voters to avoid the difficult search for a non-controversial but respected public figure.Even so, kings and queens undoubtedly have a downside. Symbolic of national unity as they claim to be, their very history—and sometimes the way they behave today –embodies outdated and indefensible privileges and inequalities. At a time when Thomas Piketty and other economists are warning of rising inequality and the increasing power of inherited wealth, it is bizarre that wealthy aristocratic families should still be the symbolic heart of modern democratic states.The most successful monarchies strive to abandon or hide their old aristocratic ways. Princes and princesses have day-jobs and ride bicycles, not horses (or helicopters). Even so, these are wealthy families who party with the international 1%, and media intrusiveness makes it increasingly difficult to maintain the right image.While Euro pe’s monarchies will no doubt be smart enough to survive for some time to come, it is the British royals who have most to fear from the Spanish example.It is only the Queen who has preserved the monarchy’s reputation with her rather ordinary (if well-heeled) granny style. The danger will come with Charles, who has both anexpensive taste of lifestyle and a pretty hierarchical view of the world. He has failed to understand that monarchies have largely survived because they provide a service – as non-controversial and non-political heads of state. Charles ought to know that as English history shows, it is kings, not republicans, who are the monarchy’s worst enemies.21. According to the first two Paragraphs, King Juan Carlos of Spain[A] used turn enjoy high public support[B] was unpopular among European royals[C] cased his relationship with his rivals[D]ended his reign in embarrassment22. Monarchs are kept as heads of state in Europe mostly[A] owing to their undoubted and respectable status[B] to achieve a balance between tradition and reality[C] to give voter more public figures to look up to[D]due to their everlasting political embodiment23. Which of the following is shown to be odd, according to Paragraph 4?[A] Ari stocrats’ excessive reliance on inherited wealth[B] The role of the nobility in modern democracies[C] The simple lifestyle of the aristocratic families[D]The nobility’s adherence to their privileges24. The British royals “have most to fear” because Charles[A] takes a rough line on political issues[B] fails to change his lifestyle as advised[C] takes republicans as his potential allies[D] fails to adapt himself to his future role25. Which of the following is the best title of the text?[A] Carlos, Glory and Disgrace Combined[B] Charles, Anxious to Succeed to the Throne[C] Carlos, a Lesson for All European Monarchs[D]Charles, Slow to React to the Coming ThreatsText 2Just how much does the Constitution protect your digital data? The Supreme Court will now consider whether police can search the contents of a mobile phone without a warrant if the phone is on or around a person during an arrest.California has asked the justices to refrain from a sweeping ruling particularly one that upsets the old assumption that authorities may search through the possessions of suspects at the time of their arrest. It is hard, the state argues, for judges to assess the implications of new and rapidly changing technologies.The court would be recklessly modest if it followed California’s advice. Enough of the implications are discernable, even obvious, so that the justices can and should provide updated guidelines to police, lawyers and defendants.They should start by discard ing California’s lame argument that exploring the contents of a smart phone — a vast storehouse of digital information — is similar to, say, rifling through a suspect’s purse. The court has ruled that police don’t violate the Fourth Amendment when they sif t through the wallet or pocketbook of an arrestee without a warrant. But exploring one’s smart phone is more like entering his or her home. A smart phone may contain an arrestee’s reading history, financial history, medical history and comprehensive records of recent correspondence. The development of “cloud computing,” meanwhile, has made that exploration so much the easier.Americans should take steps to protect their digital privacy. But keeping sensitive information on these devices is increasingly a requirement of normal life. Citizens still have a right to expect private documents to remain private and protected by the Constitution’s prohibition on unreasonable searches.As so often is the case, stating that principle doesn’t ease the challenge of line-drawing. In many cases, it would not be overly onerous for authorities to obtain a warrant to search through phone contents. They could still invalidate Fourth Amendment protections when facing severe, urgent circumstances, and they could take reasonable measures to ensure that phone data are not erased or altered while a warrant is pending. The court, though, may want to allow room for police to cite situations where they are entitled to more freedom.But the justices should not swallow California’s argument whole. New, disruptive technology sometimes demands novel applications of the Constitution’s protections. Orin Kerr, a law professor, compares the explosion and accessibility of digital information in the 21st centurywith the establishment of automobile use as a virtual necessity of life in the 20th: The justices had to specify novel rules for the new personal domain of the passenger car then; they must sort out how the Fourth Amendment applies to digital information now.26. The Supreme Court will work out whether, during an arrest, it is legitimate to[A] prevent suspects from deleting their phone contents.[B] search for suspects’ mobile phones without a warrant.[C] check suspects’ phone contents without being authorized.[D]prohibit suspects from using their mobile phones.27. The author’s attitude toward California’s argument is one of[A] disapproval.[B] indifference.[C] tolerance.[D]cautiousness.28. The author believes that exploring one’s phone contents is comparable to[A] getting into one’s residence.[B] handling one’s historical records.[C] scanning one’s correspondences.[D] going through one’s wallet.29. In Paragraph 5 and 6, the author shows his concern that[A] principles are hard to be clearly expressed.[B] the court is giving police less room for action.[C] citizens’ privacy is not effectively protected.[D] phones are used to store sensitive information.30. Orin Kerr’s comparison is quoted to indicate that[A] the Constitution should be implemented flexibly.[B] new technology requires reinterpretation of the Constitution.[C]California’s argument violates principles of the Constitution.[D]principles of the Constitution should never be alteredText 3The journal Science is adding an extra round of statistical checks to its peer-review process, editor-in-chief Marcia McNutt announced today. The policy follows similar efforts from other journals, after widespread concern that basic mistakes in data analysis are contributing to the irreproducibility of many published research findings.“Readers must have confidence in the conclusions published in our journal,” writes McNutt in an editorial. Working with the American Statistical Association, the journal has appointed seven experts to a statistics board of reviewing editors(SBoRE). Manuscript will be flagged up for additional scrutiny by the journal’s internal editors, or by its existing Board of Reviewing Editors or by outside peer reviewers. The SBoRE panel will then find external statisticians to review these manuscripts.Asked whether any particular papers had impelled the change, McNutt said: “Thecreation of the ‘statistics board’ was motivated by concerns broadly with the application of statistics and data ana lysis in scientific research and is part of Science’s overall drive to increase reproducibility in the research we publish.”Giovanni Parmigiani, a biostatistician at the Harvard School of Public Health, a member of the SBoRE group. He says he expects th e board to “play primarily an advisory role.” He agreed to join because he “found the foresight behind the establishment of the SBoRE to be novel, unique and likely to have a lasting impact. This impact will not only be through the publications in Science itself, but hopefully through a larger group of publishing places that may want to model their approach after Science.”John Ioannidis, a physician who studies research methodology, says that the policy is “a most welcome step forward” and “long overdue.” “Most journals are weak in statistical review, and this damages the quality of what they publish. I think that, for the majority of scientific papers nowadays, statistical review is more essential than expert review,” he says. But he noted that biomedical journals such as Annals of Internal Medicine, the Journal of the American Medical Association and The Lancet pay strong attention to statistical review.Professional scientists are expected to know how to analyze data, but statistical errors are alarmingly common in published research, according to David Vaux, a cell biologist. Researchers should improve their standards, he wrote in 2023, but journals should also take a tougher line, “engaging reviewers who are statistically literate and editors who can verify the process”. Vaux says that Science’s idea to pass some papers to statisticians “has some merit, but aweakness is that it relies on the board of reviewing editors to identify ‘the papers that need scrutiny’ in the first place”.31. It can be learned from Paragraph 1 that[A] Science intends to simplify their peer-review process.[B] journals are strengthening their statistical checks.[C] few journals are blamed for mistakes in data analysis.[D] lack of data analysis is common in research projects.32. The phrase “flagged up” (Para. 2) is the closest in meaning to[A] found.[B] marked.[C] revised.[D] stored.33. Giovanni Parmigiani believes that the establishment of the SBoRE may[A] pose a threat to all its peers.[B] meet with strong opposition.[C] increase Science’s circulation.[D]set an example for other journals.34. David Vaux holds that what Science is doing now[A] adds to researchers’ workload.[B] diminishes the role of reviewers.[C] has room for further improvement.[D]is to fail in the foreseeable future35. Which of the following is the best title of the text?[A] Science Joins Push to Screen Statistics in Papers.[B] Professional Statisticians Deserve More Respect[C] Data Analysis Finds Its Way onto Editors’ Desks[D] Statisticians Are Coming Back with ScienceText 4Two years ago, Rupert Murdoch’s daughter ,Elisabeth ,spoke of the “unsettling dearth of integrity across so many of our institutions” Integrity had collapsed, she argued, because of a collective acceptance that the only “sorting mechanism ”in society should be profit and the market .But “it’s us ,human beings ,we the people who create the society we want ,not profit ”.Driving her point home, she continued: “It’s increasingly apparent that the absence of purpose, of a moral language within government, media or business could become one of the most dangerous foals for capitalism and freedom.” This same absence of moral purpose was wounding companies such as News International ,shield thought ,making it more likely that it would lose its way as it had with widespread illegal telephone hacking .As the hacking trial concludes –finding guilty ones-editor of the News of the World, Andy Coulson, for conspiring to hack phones ,and finding his predecessor, Rebekah Brooks, innocent of the same charge –the winder issue of dearth of integrity still standstill, Journalists areknown to have hacked the phones of up to 5,500 people .This is hacking on an industrial scale ,as was acknowledged by Glenn Mulcaire, the man hired by the News of the World in 2023 to be the point person for phone hacking. Others await trial. This long story still unfolds.In many respects, the dearth of moral purpose frames not only the fact of such widespread phone hacking but the terms on which the trial took place .One of the astonishing revelations was how little Rebekah Brooks knew of what went on in her newsroom, wow little she thought to ask and the fact that she never inquired wow the stories arrived. The core of her successful defence was that she knew nothing.In today’s world, title has become normal that well—paid executives should not be accountable for what happens in the organizations that they run perhaps we should not be so surprised. For a generation, the collective doctrine has been that the sorting mechanism of society should be profit. The words that have mattered are efficiency, flexibility, shareholder value, business–friendly, wealth generation, sales, impact and, in newspapers, circulation. Words degraded to the margin have been justice fairness, tolerance, proportionality and accountability.The purpose of editing the News of the World was not to promote reader understanding to be fair in what was written or to betray any common humanity. It was to ruin lives in the quest for circulation and impact. Ms Brooks may or may not have had suspicions about how her journalists got their stories, but she asked no questions, gave no instructions—nor received traceable, recorded answers.36. According to the first two paragraphs, Elisabeth was upset by[A] the consequences of the current sorting mechanism[B] companies’ financial loss due to immoral practices.[C] governmental ineffectiveness on moral issues.[D]the wide misuse of integrity among institutions.37. It can be inferred from Paragraph 3 that[A] Glem Mulcaire may deny phone hacking as a crime[B] more journalists may be found guilty of phone hacking.[C] Andy Coulson should be held innocent of the charge.[D] phone hacking will be accepted on certain occasions.38. The author believes the Rebekah Books’s deference[A] revealed a cunning personality[B] centered on trivial issues[C] was hardly convincing[D] was part of a conspiracy39. The author holds that the current collective doctrine shows[A] generally distorted values[B] unfair wealth distribution[C] a marginalized lifestyle[D] a rigid moral cote40. Which of the following is suggested in the last paragraph?[A] The quality of writing is of primary importance.[B] Common humanity is central news reporting.[C] Moral awareness matters in exciting a newspaper.[D] Journalists need stricter industrial regulations.Part BDirections:In the following text, some sentences have been removed. For Questions 41-45, choose the most suitable one from the fist A-G to fit into each of the numbered blanks. Mark your answers on ANSWER SHEET. (10 points)How does your reading proceed? Clearly you try to comprehend, in the sense of identifying meanings for individual words and working out relationships between them, drawing on your explicit knowledge of English grammar (41) ______you begin to infer a context for the text, for instance, by making decisions about what kind of speech event is involved: who is making the utterance, to whom, when and where.The ways of reading indicated here are without doubt kinds of of comprehension. But they show comprehension to consist not just passive assimilation but of active engagement inference and problem-solving. You infer information you feel the writer has invited you to grasp by presenting you with specific evidence and cues (42) _______Conceived in this way, comprehension will not follow exactly the same track for each reader. What is in question is not the retrieval of an absolute, fixed or “true” meaning that can beread off and clocked for accuracy, or some timeless relation of the text to the world. (43) _______ Such background material inevitably reflects who we are, (44) _______This doesn’t, however, make interpretation merely relative or even pointless. Precisely because readers from different historical periods, places and social experiences produce different but overlapping readings of the same words on the page-including for texts that engage with fundamental human concerns-debates about texts can play an important role in social discussion of beliefs and values.How we read a given text also depends to some extent on our particular interest in reading it. (45)_______such dimensions of read suggest-as others introduced later in the book will also do-that we bring an implicit (often unacknowledged) agenda to any act of reading. It doesn’t then necessarily follow that one kind of reading is fuller, more advanced or more worthwhile than another. Ideally, different kinds of reading inform each other, and act as useful reference points for and counterbalances to one another. Together, they make up the reading component of your overall literacy or relationship to your surrounding textual environment.[A] Are we studying that text and trying to respond in a way that fulfils the requirement of a given course? Reading it simply for pleasure? Skimming it for information? Ways of reading on a train or in bed are likely to differ considerably from reading in a seminar room.[B] Factors such as the place and period in which we are reading, our gender ethnicity, age and social class will encourage us towards certain interpretation but at the same time obscure or even close off others.[C] If you are unfamiliar with words or idioms, you guess at their meaning, using cluespresented in the contest. On the assumption that they will become relevant later, you make a mental note of discourse entities as well as possible links between them.[D]In effect, you try to reconstruct the likely meanings or effects that any given sentence, image or reference might have had: These might be the ones the author intended.[E]You make further inferences, for instance, about how the test may be significant to you, or about its validity—inferences that form the basis of a personal response for which the author will inevitably be far less responsible.[F]In plays，novels and narrative poems, characters speak as constructs created by the author, no t necessarily as mouthpieces for the author’s own thoughts.[G]Rather, we ascribe meanings to test on the basis of interaction between what we might call textual and contextual material: between kinds of organization or patterning we perceive in a text’s formal structures (so especially its language structures) and various kinds of background, social knowledge, belief and attitude that we bring to the text.Section III TranslationDirections:Read the following text carefully and then translate the underlined segments into Chinese. Your translation should be written clearly on ANSWER SHEET. (10 points) Within the span of a hundred years, in the seventeenth and early eighteenth centuries, a tide of emigration—one of the great folk wanderings of history—swept from Europe to America.46) This movement, driven by powerful and diverse motivations, built a nation out of a wilderness and, by its nature, shaped the character and destiny of an uncharted continent.47) The United States is the product of two principal forces-the immigration of European peoples with their varied ideas, customs, and national characteristics and the impact of a new country which modified these traits. Of necessity, colonial America was a projection of Europe. Across the Atlantic came successive groups of Englishmen, Frenchmen, Germans, Scots, Irishmen, Dutchmen, Swedes, and many others who attempted to transplant their habits and traditions to the new world.48) But, the force of geographic conditions peculiar to America, the interplay of the varied national groups upon one another, and the sheer difficulty of maintaining old-world ways in a raw, new continent caused significant changes. These changes were gradual and at first scarcely visible. But the result was a new social pattern which, although it resembled European society in many ways, had a character that was distinctly American.49) The first shiploads of immigrants bound for the territory which is now the United States crossed the Atlantic more than a hundred years after the 15th- and 16th-century explorations of North America. In the meantime, thriving Spanish colonies had been established in Mexico, the West Indies, and South America. These travelers to North America came in small, unmercifully overcrowded craft. During their six- to twelve-week voyage, they subsisted on barely enough food allotted to them. Many of the ship were lost in storms, many passengers died of disease, and infants rarely survived the journey. Sometimes storms blew the vessels far off their course, andoften calm brought unbearably long delay.“To the anxious travelers the sight of the American sh ore brought almost inexpressible relief.” said one recorder of events, “The air at twelve leagues’ distance smelt as sweet as a new-blown garden.” The colonists’ first glimpse of the new land was a sight of dense woods. 50) The virgin forest with its richness and variety of trees was a veritable real treasure-house which extended from Maine all the way down to Georgia. Here was abundant fuel and lumber. Here was the raw material of houses and furniture, ships and potash, dyes and naval stores.Section IV WritingPart A51. Directions:You are going to host a club reading session. Write an email of about 100 words recommending a book to the club members.You should state reasons for your recommendation.You should write neatly on the ANSWER SHEET.Do not sign your own name at the end of the letter. Use Li Ming instead.Do not write the address. (10 points)Part B52. Directions:Write an essay of 160-200 words based on the following drawing. In your essay you should1) describe the drawing briefly2) explain its intended meaning, and3) give your commentsYou should write neatly on ANSWER SHEET. (20 points)时代旳聚会参照答案及详细解析I cloze1. [A] when [B] why [C] how [D] what【答案】[D] what【解析】该题考察旳是语法知识。
高一英语跨文化交际策略单选题40题1.In some Western countries, nodding the head means “yes”, while in some Asian countries, shaking the head means “yes”. In India, people often shake their heads to show ___.A.agreementB.disagreementC.uncertaintyD.impatience答案：A。
在印度，人们摇头通常表示同意。
选项B“disagreement”是不同意；选项C“uncertainty”是不确定；选项D“impatience”是不耐烦。
2.In the United States, a thumbs-up sign usually means ___.A.approvalB.requestC.warningD.disapproval答案：A。
在美国，竖起大拇指通常表示赞成、认可。
选项B“request”是请求；选项C“warning”是警告；选项D“disapproval”是不赞成。
3.In Japan, bowing is a common form of greeting. A deep bow usually indicates ___.A.respectB.familiarityC.indifferenceD.disrespect答案：A。
在日本，鞠躬是常见的问候方式。
深深鞠躬通常表示尊敬。
选项B“familiarity”是熟悉；选项C“indifference”是冷漠；选项D“disrespect”是不尊敬。
4.In some Middle Eastern countries, pointing with the index finger is considered ___.A.politeB.rudeC.friendlyD.formal答案：B。
2024年高二英语学科全球合作研究的合作机制构建分析单选题30题1.International cooperation is crucial for addressing global challenges. The ______ of different countries is essential.A.effortsanizationsC.cooperationsD.initiatives答案：B。
“国际合作对于应对全球挑战至关重要。
不同国家的组织是必不可少的。
”A 选项“efforts”努力；C 选项“cooperations”合作，此处与前文重复；D 选项“initiatives”倡议。
根据语境，这里强调不同国家的组织，所以选B。
2.Global cooperation requires strong ______ among nations.A.associationsB.partnershipsC.connectionsD.relationships答案：B。
“全球合作需要国家之间强大的伙伴关系。
”A 选项“associations”协会；C 选项“connections”联系；D 选项“relationships”关系，而伙伴关系更能体现全球合作的需求，所以选B。
3.The success of global cooperation depends on effective ______.A.coordinationsB.arrangementsanizationsD.plans答案：C。
“全球合作的成功取决于有效的组织。
”A 选项“coordinations”协调；B 选项“arrangements”安排；D 选项“plans”计划。
这里强调组织的重要性，所以选C。
4.In global cooperation, ______ play an important role in promoting common development.A.institutionspaniesC.factoriesD.schools答案：A。
擅长作战样式评价英文Evaluating Combat Styles: A Technical Analysis.In the realm of military strategy, the evaluation of combat styles is crucial for achieving success on the battlefield. Different styles of warfare have their unique strengths and weaknesses, and understanding these nuances is essential for making informed decisions. This article aims to provide a technical analysis of various combat styles, exploring their advantages, disadvantages, and applications in modern warfare.1. Blitzkrieg (Lightning War)。
Blitzkrieg, or "lightning war," was a tactic pioneered by Germany in the early 20th century. It emphasized rapid, surprise attacks using mobile armored units and motorized infantry to quickly overwhelm enemy defenses. Blitzkrieg's main strengths lie in its speed and surprise, which can shatter enemy morale and collapse resistance quickly.However, this style is highly dependent on technology and logistics, and it can be vulnerable to enemy counterattacks if the initial assault fails to achieve its objectives.2. Guerilla Warfare.Guerilla warfare involves small, mobile units attacking enemy supply lines, rear areas, and other vulnerabletargets to disrupt and wear down the enemy. This style excels in prolonged conflicts where conventional forces may be outnumbered or outgunned. Guerilla warfare requires significant intelligence gathering, local support, and adaptability, but it can be highly effective in wearing down enemy morale and resources. However, it also has the risk of escalating into full-scale conflict if the enemy responds with disproportionate force.3. Attrition Warfare.Attrition warfare involves the gradual wearing down of the enemy through sustained combat, often over an extended period. This style aims to exhaust the enemy's resources,manpower, and morale through continuous attacks and defense. Attrition warfare is effective when both sides are evenly matched in terms of technology and resources, and it can be used to grind down enemy resistance over time. However, it can also lead to staggering losses on both sides and isoften slow and costly.4. Maneuver Warfare.Maneuver warfare focuses on using speed, mobility, and deception to outmaneuver the enemy. This style emphasizesthe use of indirect attacks, feints, and surprise maneuvers to create advantageous positions and gain the initiative. Maneuver warfare requires highly trained and mobile forces that can adapt quickly to changing situations. It is effective against enemy forces that are slower or less mobile, but it can also be risky if the enemy anticipates and counters the maneuvers.5. Information Warfare.Information warfare, or cyberwarfare, involves the useof technology to disrupt, degrade, or destroy enemy information systems. This style aims to gain a strategic advantage by manipulating information, disrupting enemy communications, and targeting critical infrastructure. Information warfare requires highly skilled operators and advanced technology, but it can be devastatingly effective in modern conflicts where information is critical to success. However, it also raises significant ethical and legal concerns about the use of force against civilian targets.In conclusion, the evaluation of combat styles is crucial for military planners and commanders. Understanding the strengths and weaknesses of different styles allows for more informed decisions about strategy and tactics. While no single style is perfect, a combination of different approaches can be effective in achieving military objectives. The key is to adapt and innovate, continuously learning from past conflicts and applying that knowledge to future battles.。
a r X i v :c s /0405111v 2 [c s .C R ] 27 N o v 2004Attrition Defenses for a Peer-to-Peer Digital Preservation SystemTJ GiuliStanford University,CAPetros ManiatisIntel Research,Berkeley,CAMary BakerHP Labs,Palo Alto,CADavid S.H.RosenthalStanford University Libraries,CAMema RoussopoulosHarvard University,Cambridge,MAAbstractIn peer-to-peer systems,attrition attacks include both traditional,network-level denial of service attacks as well as application-level attacks in which malign peers conspire to waste loyal peers’resources.We describe several defenses for LOCKSS,a peer-to-peer digital preservation system,that help ensure that application-level attacks even from powerful adversaries are less effective than simple network-level attacks,and that network-level attacks must be intense,wide-spread,and prolonged to impair the system.$Revision: 1.317$1IntroductionDenial of Service (DoS)attacks are among the most dif-ficult for distributed systems to resist.Distinguishing le-gitimate requests for service from the attacker’s requests can be tricky,and devoting substantial effort to doing so can easily be self-defeating.The term DoS was in-troduced by Needham [32]with a broad meaning but over time it has come to mean high-bit-rate network-level flooding attacks [22]that rapidly degrade the usefulness of the victim system.In addition to DoS,we use the term attrition to include also moderate-or low-bit-rate application-level attacks that gradually impair the victim system.The mechanisms described in this paper are aimed at equipping the LOCKSS 1peer-to-peer (P2P)digital preservation system to resist attrition attacks.The sys-tem is in use at about 80libraries worldwide;publishers of about 2000titles have endorsed its use.Cooperation among peers reduces the cost and increases the reliabil-ity of preservation,eliminates the need for backup,and greatly reduces other operator interventions.A loyal (non-malign)peer participates in the LOCKSS system for two reasons:to achieve regular reassurancecrux of attrition attacks and their defenses,we extend our prior evaluation[29]to deal with numerous con-currently preserved archival units of content competing with each other for resources.Finally,resource over-provisioning is essential in defending against attrition attacks.Our contribution is the ability to put an upper bound on the amount of over-provisioning required to defend the LOCKSS system from an arbitrarily power-ful attrition adversary.Our defenses may not all be im-mediately applicable to all P2P applications,but we be-lieve that many systems may benefit from a subset of de-fenses,and that our analysis of the effectiveness of these defenses is more broadly useful.In the rest of this paper,wefirst describe our applica-tion.We continue by outlining how we would like this application to behave under different levels of attrition attack.We give an overview of the LOCKSS protocol, describing how it incorporates each of our attrition de-fenses.We then explain the results of a systematic explo-ration of simulated attacks against the resulting design, showing that it successfully defends against attrition at-tacks at all layers,from the network level up through the application protocol.2The ApplicationIn this section,we provide an overview of the digital preservation problem for academic publishing,the prob-lem that LOCKSS seeks to solve.We then present and justify the set of design goals required of any solution to this problem,setting the stage for our approach in subse-quent sections.Academic publishing has migrated to the Web[42], placing society’s scientific and cultural heritage at a vari-ety of risks such as confused provenance,accidental edit-ing by the publisher,storage corruption,failed backups, government or corporate censorship,vandalism,and de-liberate rewriting of history.The LOCKSS system was designed[36]to provide librarians with the tools they need to preserve their community’s access to journals and other Web materials.Any solution must meet six stringent requirements. First,since under US law[16]copyright Web content can only be preserved with the owner’s permission,the so-lution must accommodate the publishers’interests.Re-quiring publishers,for example,to offer perpetual no-fee access or digital signatures on content makes them reluctant to give that permission.Second,a solution must be extremely cheap in terms of hardware,operating cost,and human expertise.Few libraries could afford[3] a solution involving handling and securely storing off-line media,but most can afford the few cheap off-the-shelf PCs that provide sufficient storage for tens of thou-sands of journal-years.Third,the existence of cheap,reliable storage cannot be assumed;affordable storage is unreliable[21,35].Fourth,a solution must have a long time horizon.Auditing content against stored dig-ital signatures,for example,assumes not only that the cryptosystem will remain unbroken,but also that the se-crecy,integrity,and availability of the keys are guaran-teed for decades.Fifth,a solution must anticipate ad-versaries capable of powerful attacks sustained over long periods;it must withstand these attacks,or at least de-grade slowly and gracefully while providing unambigu-ous warnings[34].Sixth,a solution must not require a central locus of control or administration,if it is to with-stand concentrated technical or legal attacks.Two different architectures have been proposed for preserving Web journals.On one hand,trusted third party archives require publishers to grant the archive per-mission,under certain circumstances,to republish their content.It has proved very difficult to persuade pub-lishers to do so[5].In the LOCKSS system,on the other hand,publishers need only grant their subscribing libraries permission to supply their own content replica to their local readers.This has been the key to obtaining permission from publishers.It is thus important to note that our goal is not to minimize the number of replicas consistent with content safety.Instead,we strive to min-imize the per-replica cost of maintaining a large number of replicas.We trade extra replicas for fewer lawyers,an easy decision given their relative costs.The LOCKSS design is extremely conservative,mak-ing few assumptions about the infrastructure.Although we believe this is appropriate for a digital preservation system,less conservative assumptions are certainly pos-sible.Taking increased risk can increase the amount of content that can be preserved with given computa-tional power.For example,the availability of limited amounts of reliable,write-once memory would allow au-dits against local hashes,the availability of a reliable public key infrastructure might allow publishers to sign their content and peers to audit against the signatures, and so on.Conservatively,the assumptions underlying such optimizations could be violated without warning at any time;the write-once memory might be corrupted or mishandled or a private key might leak.Thus,designs us-ing these optimizations would still need the audit mech-anism as a fall-back.The more a peer operator can do to avoid local failures the better the system works,but our conservative design principles lead us to focus on mech-anisms that minimize dependence on these efforts. With this specific application in mind,we tackle the “abstract”problem of auditing and repairing replicas of distinct archival units or AUs(a year’s run of an on-line journal,in our target application)preserved by a popu-lation of peers(libraries)in the face of attrition attacks. For each AU it preserves,a peer starts out with its own,correct replica(obtained from the publisher’s Web site), which it can only use to satisfy local read requests(from local patrons)and to assist other peers with replica re-pairs.In the rest of this paper we refer to AUs,peers, and replicas,rather than journals and libraries.3System ModelIn this section we present the adversary we model,our security goals for the system,and our defensive frame-work.3.1Adversary ModelIn keeping with our conservative design philosophy,we assume a powerful adversary with several important abil-ities.Pipe stoppage is his ability to prevent communi-cation with victim peers for extended periods byflood-ing links with garbage packets or using more sophisti-cated techniques[25].Total information awareness al-lows him to control and monitor all of his resources in-stantaneously.He has unconstrained identities in that he can purchase or spoof unlimited network identities.In-sider information allows him complete knowledge of his victims’system parameters and resource commitments. Masquerading means that loyal peers cannot detect him, as long as he follows the protocol.Finally,he has unlim-ited computational resources,though he is polynomially bounded in his computations(i.e.,he cannot invert cryp-tographic functions).The adversary employs these capabilities in effortless and effortful attacks.An effortless attack requires no measurable computational effort from the attacker and includes traditional DoS attacks such as pipe stoppage. An effortful attack requires the attacker to invest in the system and therefore requires computational effort. 3.2Security GoalsThe overall goal of the LOCKSS system is to maintain a high probability that the consensus of peers reflects the correct AU,and a high probability that a reader accesses good data.In contrast,an attrition adversary’s goal is to decrease these probabilities significantly by preventing peers from auditing their replicas for a long time,long enough for undetected storage problems such as“bit rot”to occur.Severe pipe stoppage attacks in the wild last for days or weeks[31].Our goal is to ensure that,in the very least,the LOCKSS system withstands such attacks sus-tained over months.Beyond pipe stoppage,attackers must use protocol messages to some extent.We seek to ensure the following three conditions.First,a peer man-ages its resources so as to prevent exhaustion no matter how much effort is exerted by however many identities request service.Second,when deciding which requests to service,a peer gives preference to requests from those likely to behave properly(i.e.,“ostensibly legitimate”). And third,at every stage of a protocol exchange,an os-tensibly legitimate attacker expends commensurate effort to that which he imposes upon the defenders.3.3Defensive FrameworkWe seek to curb the adversary’s success by modeling a peer’s processing of inbound messages as a series of filters,each costing a certain amount to apply.A mes-sage rejected by afilter has no further effect on the peer, allowing us to estimate the cost of eliminating whole classes of messages from further consideration.Eachfil-ter increases the effort a victim needs to defend itself,but limits the effectiveness of some adversary capability. The bandwidthfilter models a peer’s network connec-tion.It represents the physical limits on the rates of inbound messages that an adversary can force upon his victims.The admission controlfilter takes inbound mes-sages at the maximum rate supported by the bandwidth filter and further limits them to match the maximum rate at which a peer expects protocol traffic from legitimate senders,favoring known peer identities.This curbs the adversary’s use of unlimited identities and prevents him from applying potentially unconstrained computational resources upon a victim.The effort balancingfilters en-sure that effort imposed upon a victim by ostensibly le-gitimate traffic is balanced by correspondingly high ef-fort borne by the attacker,making it costly for a resource-constrained adversary to masquerade as a legitimate peer. We show in Section7.4that the most effective strat-egy for effortful attacks is to emulate legitimacy,and that even this has minimal effect on the utility of the system. Effortless attacks,such as traditional distributed DoS (DDoS)attacks,are more effective but must be main-tained for a long time against most of the peer population to degrade the system significantly(Section7.2).4The LOCKSS Replica Auditing and Re-pair ProtocolThe LOCKSS audit process operates as a sequence of “opinion polls”conducted by every peer on each of its AU replicas.At intervals,typically every3months,a peer(the poller)constructs a random subset(i.e.,sam-ple)of the peer population that it knows are preserv-ing an AU,and invites those peers as voters into a poll. Each voter individually hashes a poller-supplied nonce and its replica of the AU to produce a fresh vote,which the poller tallies.If the poller is outvoted in a landslide (e.g.,it disagrees with80%of the votes),it assumes itsFigure1:A time-line of a poll,showing the message exchange between the poller and a voter.replica is corrupt and repairs it from a disagreeing voter. The roles of poller and voter are distinct,but every peer plays both.The general structure of a poll follows the time-line of Figure1.A poll consists of two phases:the vote solici-tation phase and the evaluation phase.In the vote solic-itation phase the poller requests and obtains votes from as many voters in its sample of the population as pos-sible.Then the poller begins the evaluation phase,dur-ing which it compares these votes to its own replica,one hashed content block at a time,and tallies them.If the hashes disagree the poller may request repair blocks from its voters and re-evaluate the block.If in the eventual tally,after any repairs,the poller agrees with the land-slide majority,it sends a receipt to each of its voters and immediately starts a new poll.Peers interleave making progress on their own polls and voting in other peers’polls,spreading each poll over a long period chosen so that polls on a given AU occur at a rate much higher than the rate of undetected storage problems,e.g.“bit rot.”4.1Vote SolicitationThe outcome of a poll is determined by the votes of the inner circle peers,sampled at the start of the poll by the poller from its reference list for the AU.The reference list contains mostly peers that have agreed with the poller in recent polls on the AU,and a few peers from its static friends list,maintained by the poller’s operator.A poll is considered successful if its result is based on a minimum number of inner circle votes,the quorum, which is typically10,but may change according to the application’s needs for fault tolerance.To ensure that a poll is likely to succeed,a poller invites into its poll a larger inner circle than the quorum(typically,twice as large).If atfirst try,an inner circle peer fails to respond to an invitation,or refuses it,the poller contacts a different inner circle voter,re-trying the reluctant peer later in the same vote solicitation phase.An individual vote solicitation consists of four mes-sages(see Figure1):Poll,PollAck,PollProof,and Vote. For the duration of a poll,a poller establishes an en-crypted TLS session with each voter individually,via an anonymous Diffie-Hellman key exchange.Every proto-col message is conveyed over this TLS session,either keeping the same TCP connection from message to mes-sage,or resuming the TLS session over a new one.The Poll message invites a voter to participate in a poll on an AU.The invited peer responds with a PollAck mes-sage,indicating either a refusal to participate in the poll at the time,or an acceptance of the invitation,if it can compute a vote within a predetermined time allowance. The voter commits and reserves local resources to that effect.The PollProof message supplies the voter with a random nonce to be used during vote construction.To compute its vote,the voter uses a cryptographic hash function(e.g.,SHA-1)to hash the nonce supplied by the poller,followed by its replica of the AU,block by block. The vote consists of the running hashes produced at each block boundary.Finally,the voter sends its vote back to the poller in a Vote message.These messages also contain proofs of computational effort,such as those introduced by Dwork et al.[15], sufficient to ensure that,at every protocol stage,the re-quester of a service has more invested in the exchange than the supplier of the service(see Section5.1).4.2Peer DiscoveryThe poller uses the vote solicitation phase of a poll not only to obtain votes for the current poll,but also to dis-cover new peers for its reference list from which it can solicit inner circle votes in future polls.Discovery is effected via nominations included in Vote messages.A voter picks a random subset of its cur-rent reference list,which it includes in the Vote message. The poller accumulates these nominations.When it con-cludes its inner circle solicitations,it chooses a random sample of these nominations as its outer circle.It pro-ceeds to solicit regular votes from these outer circle peers in a manner identical to that used for inner circle peers. The purpose of the votes obtained from outer circle voters is to show the“good behavior”of newly discov-ered peers.Those who perform correctly,by supplying votes that agree with the prevailing outcome of the poll, are added into the poller’s reference list at the conclu-sion of the poll;the outcome of the poll is computed only from inner-circle votes.4.3Vote EvaluationOnce the poller has accumulated all votes it could obtain from inner and outer circle voters,it begins the poll’s evaluation phase.During this phase,the poller computes,in parallel,all block hashes that each voter should have computed,if that voter’s replica agreed with the poller’s.A vote agrees with the poller on a block if the hash in the vote and that computed by the poller are the same.For each hash computed by the poller for an AU block, there are three possibilities:first,the landslide majority of inner-circle votes(e.g.,80%)agree with the poller;in this case,the poller considers the audit successful up to this block and proceeds with the next block.Second,the landslide majority of inner-circle votes disagree with the poller;in this case,the poller regards its own replica of the AU as damaged,obtains a repair from one of the dis-agreeing voters(via the RepairRequest and Repair mes-sages),and reevaluates the block hoping tofind itself in the landslide majority,as above.Third,if there is no landslide majority of agreeing or disagreeing votes,the poller deems the poll inconclusive,raising an alarm that requires attention from a human operator. Throughout the evaluation phase,the poller may also decide to obtain a repair from a random voter,even if one is not required(i.e.,even if the corresponding block met with a landslide agreement).The purpose of such frivolous repairs is to prevent targeted free-riding via the refusal of repairs;voters are expected to supply a small number of repairs once they commit to participate in a poll,and are penalized otherwise(Section5.1).If the poller hashes all AU blocks without raising an alarm,it concludes the poll by sending an evaluation re-ceipt to each voter(with an EvaluationReceipt message), indicating that it will not be requesting any more repairs. The poller then updates its reference list by removing all voters whose votes determined the poll outcome and by inserting all agreeing outer-circle voters and some peers from the friends list(for details see[29]).The poller then restarts a poll on the same AU,scheduling it to conclude an inter-poll interval into the future.5LOCKSS DefensesHere we outline the attrition defenses of the LOCKSS protocol:admission control,desynchronization,and re-dundancy.These defenses raise system costs for both loyal peers and attackers,but favor ostensible legiti-macy.Given a constant amount of over-provisioning, loyal peers continue to operate at the necessary rate re-gardless of the attacker’s power.Many systems over-provision resources to protect performance from known worst-case behavior(e.g.,the Unixfile system[30]). 5.1Admission ControlThe purpose of the admission control defense is to ensure that a peer can control the rate at which it considers poll invitations from others,favoring invitations from those who operate at roughly the same rate as itself and pe-nalizing others.We implement admission control using three mechanisms:rate limitation,first-hand reputation, and effort balancing.Rate Limitation:Without limits on the rate at which they attempt to service requests,peers can be over-whelmed byfloods of ostensibly valid requests.Rate Limitation suggests that peers should initiate and sat-isfy requests no faster than necessary rather than as fast as possible.Because readers access only their lo-cal LOCKSS peer,the audit and repair protocol is not subject to end-users’unpredictable request patterns.The protocol can proceed at its own pace,providing an inter-esting test case for rate limitation.We identify three possible attacks based on deviation from the necessary rate of polling.A poll rate adversary would seek to trick victims into either decreasing(e.g., by causing back-off behavior)or increasing(e.g.,in an attempt to recover from a failed poll)their rate of calling polls.A pollflood adversary would seek,under a multi-tude of identities,to invite victims into as many frivolous polls as possible hoping to crowd out the legitimate poll requests and thereby reduce the ability of loyal peers to audit and repair their content.A voteflood adversary would seek to supply as many bogus votes as possible hoping to exhaust loyal pollers’resources in useless but expensive proofs of invalidity.Peers defend against all these adversaries by setting their rate limits autonomously,not varying them in re-sponse to other peers’actions.Responding to adversity (inquorate polls or perceived contention)by calling polls more frequently could aggravate the problem;backing off to a lower rate of polls would achieve the adversary’s aim of slowing the detection and repair of damage;Kuz-manovic et al.[25]describe a similar attack in the context of TCP retransmission timers.Because peers do not re-act,the poll rate adversary has no opportunity to attack. The price of thisfixed rate of operation is that,absent manual intervention,a peer may take several inter-poll intervals to recover from a catastrophic storage failure. The pollflood adversary tries to get victims to over-commit their resources or at least to commit excessively to the adversary.To prevent over-commitment,peers maintain a task schedule of their promises to perform ef-fort,both to generate votes for others and to call their own polls.If the effort of computing the vote solicited by an incoming Poll message cannot be accommodated in the schedule,the invitation is refused.Furthermore, peers limit the rate at which they even consider poll invi-tations(i.e.,establishing a secure session,checking their schedule,etc.).A peer sets this rate limit for considering poll invitations according to the rate of poll invitations it sends out to others;this is essentially a self-clocking mechanism.We explain how this rate limit is enforced inthefirst-hand reputation description below.We evaluate our defenses against pollflood strategies in Section7.3. The voteflood adversary is hamstrung by the fact that votes can be supplied only in response to an invitation by the putative victim poller,and pollers solicit votes at afixed rate.Unsolicited votes are ignored.First-hand reputation:A peer locally maintains and usesfirst-hand reputation(i.e.,history)for other peers. Each peer P maintains a known-peers list,separately for each AU it preserves.The list contains an entry for ev-ery peer that P has encountered in the past,tracking its exchange of votes with that peer.The entry holds a rep-utation grade for the peer,which is one of three values: debt,even,or credit.A debt grade means that the peer has supplied P with fewer votes than P has supplied it.A credit grade means P has supplied the peer with fewer votes than the peer has supplied P.An even grade means that P and the peer are even in their recent exchanges of votes.Entries in the known-peers list“decay”with time toward the debt grade.In a protocol interaction,both the poller and a voter modify the grade they have assigned to each other de-pending on their respective behaviors.If the voter sup-plies a valid vote and valid repairs for any blocks the poller requests,then the poller increases the grade it has assigned to the voter(from debt to even,from even to credit,or from credit to credit)and the voter correspond-ingly decreases the grade it has assigned to the poller.If either the poller or the voter misbehave(e.g.,the voter commits to supplying a vote but does not,or the poller does not send a valid evaluation receipt),then the other peer decreases its grade to debt.This is similar to the re-ciprocative strategy of Feldman et al.[17],in that it pe-nalizes peers who do not reciprocate,i.e.,do not supply votes in return for the votes they receive.Peers randomly drop some poll invitations arriving from previously unknown peers and from pollers with a debt grade.Invitations from pollers with an even or credit grade are not dropped.This reputation system re-duces free-riding,as it is not possible for a peer to main-tain an even or credit grade without providing valid votes. To discourage identity whitewashing the drop probabil-ity imposed on unknown pollers is higher than that im-posed on known in-debt pollers.Furthermore,invitations from unknown or in-debt pollers are subject to a rigid rate limit;after it admits one such invitation for consid-eration,a voter enters a refractory period during which it automatically rejects all invitations from unknown or in-debt pollers.Like the known-peers list,refractory pe-riods are maintained on a per AU basis.Consequently, during every refractory period,a voter admits at most one invitation from unknown or in-debt peers,plus at most one invitation from each of its fellow peers with a credit or even grade.Since credit and even grades decay with time,the total“liability”of a peer in the number of in-vitations it must admit per refractory period is limited to a small constant number.As a result,the duration of the refractory period is inversely proportional to the rate limit imposed by the peer on the poll invitations that it considers for each AU it preserves.Continuous triggering of the refractory period can stop a victim voter from accepting invitations from unknown peers who are loyal;this can limit the choices a poller has in potential voters to peers that know the poller al-ready.To reduce this impediment to diversity,we in-stitute the concept of peer introductions.A peer may introduce peers that it considers loyal to others;peers introduced in this way can bypass random drops and re-fractory periods.Introductions are bundled along with nominations during the regular discovery process(Sec-tion4.2).Specifically,a poller randomly partitions the peer identities in a Vote message into outer circle nomi-nations and introductions.A poll invitation from an in-troduced peer is treated as if coming from a known peer with an even grade.This unobstructed admission con-sumes the introduction in such a way that at most one in-troduction is honored per(validly voting)introducer,and unused introductions do not accumulate.Specifically, when consuming the introduction of peer B by peer A for AU X,all other introductions of other introducees by peer A for AU X are“forgotten,”as are all introduc-tions of peer B for X by other introducers.Furthermore, introductions by peers who have entered and left the ref-erence list are also removed,and the maximum number of outstanding introductions is capped.Effort Balancing:If a peer expends more effort to re-act to a protocol message than the sender of that message did to generate and transmit it,then an attrition attack need consist only of aflow of ostensibly valid protocol messages,enough to exhaust the victim peer’s resources. We adapt the ideas of pricing via processing[15]to discourage such attacks from resource-constrained ad-versaries by effort balancing our protocol.We inflate the cost of a request by requiring it to include a proof of com-putational effort sufficient to ensure that the total cost of generating the request exceeds the cost to the supplier of both verifying the effort proof and satisfying the re-quest.We favor Memory-Bound Functions(MBF)[14] rather than CPU-bound schemes such as“client puz-zles”[12]for this purpose,because the spread in memory system performance is smaller than that of CPU perfor-mance[13].Note that an adversary with ample compu-tational resources is not hindered by effort balancing. Applying an effort balancingfilter at each step of a multi-step protocol defends against three attack patterns:first,desertion strategies in which the attacker stops tak-ing part some way through the protocol,having spent less effort in the process than the effort inflicted upon。
