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94. When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast people is tested for cocaine use, the vast majority of those who test positive will be people who have used cocaine.

A reasoning error in the argument is that the argument

A. attempts to infer a value judgment from purely factual premises
B. attributes to every member of the population the properties of the average member of the population
C. fails to take into account what proportion of the population have used cocaine
D. ignores the fact that some cocaine users do not test positive
E. advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine

CR will get more interesting when math is involved. The most seen math problem in GMAT CR is percentage. What ETS wants to test is whether you can distinguish between absolute value and relative value, e.g. percentage.
What you need to remember is that higher percentage in CR does not indicate that the absolution number or quantity will be higher compared to lower percentage. To the contrary, higher percentage always has smaller numbers or quantity.
In this question, the conclusion is the last sentence. The premises are that 5% of non-users and 99% of users are tested positive. The argument fails to consider the composition of population and makes an unwarranted assumption that among a random group of people, non-users are less than 99/5 of users. X: non-users Y: users. 5%X < 99%Y è x<99/5Y. If this proportion is not true, the argument does not hold.
So you need to know whether the question is about absolute value or relative value. If it is about relative value, you need to know what the BASE is. If comparison is involved, you need to find out the relationship between the bases.

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95. Scientific research that involves international collaboration has produced papers of greater influence, as measured by the number of times a paper is cited in subsequent papers, than has research without any collaboration. Papers that result from international collaboration are cited an average of seven times, whereas papers with single authors are cited only three times on average. This difference shows that research projects conducted by international research teams are of greater importance than those conducted by single researchers.

Which one of the following is an assumption on which the argument depends?

A. Prolific writers can inflate the number of citations they receive by citing themselves in subsequent papers.
B. It is possible to ascertain whether or not a paper is the product of international collaboration by determining the number of citations it has received.
C. The number of citations a paper receives is a measure of the importance of the research it reports.
D. The collaborative efforts of scientists who are citizens of the same country do not produce papers that are as important as papers that are produced by international collaboration.
E. International research teams tend to be more generously funded than are single researchers.

In my view, the reasoning in this argument is that:
Papers that result from international collaboration are cited an average of seven times, whereas papers with single authors are cited only three times on average.à research projects conducted by international research teams are of greater importance than those conducted by single researchers.

The hidden assumption is that we can evaluate the importance of research projects by the number of times a paper is cited in subsequent papers.

Obviously, C is the best answer.

A. is out of scope. We can also have good reasons to doubt whether the prolific writers is representative enough to reflect the whole situation of the single authors.
B. the same mistake. Even we can ascertain whether or not a paper is the product of international collaboration by determining the number of citations it has received. The preceding assumption have no effect on the conclusion.
C. is the best answer.
D. is absurd. We have not known anything about the domestic or the alien authors.
E. is out of scope too. There is nothing relevant to fund in this argument.

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96. Prominent business executives often play active roles in United States presidential campaigns as fundraisers or backroom strategists, but few actually seek to become president themselves. Throughout history the great majority of those who have sought to become president have been lawyers, military leaders, or full-time politicians. This is understandable, for the personality and skills that make for success in business do not make for success in politics. Business is largely hierarchical, whereas politics is coordinative. As a result, business executives tend to be uncomfortable with compromises and power-sharing, which are inherent in politics.

Which one of the following, if true, most seriously weakens the proposed explanation of why business executives do not run for president?

A. Many of the most active presidential fundraisers and backroom strategists are themselves politicians.
B. Military leaders are generally no more comfortable with compromises and power-sharing than are business executives.
C. Some of the skills needed to become a successful lawyer are different from some of those needed to become a successful military leader.
D. Some former presidents have engaged in business ventures after leaving office.
E. Some hierarchically structured companies have been major financial supporters of candidates for president.

In my view, the reasoning in this argument is that:
business executives tend to be uncomfortable with compromises and power-sharing, which are inherent in politics  few actually seek to become president themselves.

The hidden assumption is that:
lawyers, military leaders, or full-time politicians tend to be comfortable with compromises and power-sharing.

How to weaken this explanation?
In my view, we can undermine this reasoning in this argument in two ways. On the one hand, we can find other reasons excepting for the listed explanation, such as business executives worry about the safe of the presidents, or business executives enjoy freedom, etc. On the other hand, we can rule out analogue between business executives and the listed candidate including lawyers, military leaders, or full-time politicians. That is to say, if we can sure that some of such candidates are also tired of compromises and power sharing like business executives. The reasoning will be seriously undermined.

After this analysis, we can choose B quickly.


97. A scientific theory is a good theory if it satisfies two requirements: it must accurately describe a large class of observations in terms of a model that is simple enough to contain only a few elements, and it must make definite predictions about the results of future observations. For example, Aristotle’s cosmological theory, which claimed that everything was made out of four elements---earth, air, fire, and water---satisfied the first requirement, but it did not make any definite predictions. Thus, Aristotle’s cosmological theory was not a good theory.

If all the statements in the passage are true, each of the following must also be true EXCEPT:

A. Prediction about the results of future observations must be made by any good scientific theory
B. Observation of physical phenomena was not a major concern in Aristotle’s cosmological theory.
C. For elements can be the basis of a scientific model that is simple enough to meet the simplicity criterion of a good theory.
D. A scientific model that contains many elements is not a good theory.
E. Aristotle’s cosmological theory described a large class of observations in terms of only four elements.

After analysis , we can find that the reasoning in this argument is that:
1> it must accurately describe a large class of observations in terms of a model that is simple enough to contain only a few elements and 2> it must make definite predictions about the results of future observations.&szlig;à A scientific theory is a good theory

So , we can find all of choices except B satisfied with the original meaning.

B is not mentioned in this argument , so we can conclude whether B is also true.
So B is the best answer.

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98. Compared to nonprofit hospitals of the same size, investor-owned hospitals require less public investment in the form of tax breaks, use fewer employees, and have higher occupancy levels. It can therefore be concluded that investor-owned hospitals are a better way of delivering medical care than are nonprofit hospitals.

Which one of the following, if true, most undermines the conclusion drawn above?

A. Nonprofit hospitals charge more per bed than do investor-owned hospitals.
B. Patients in nonprofit hospitals recover more quickly than do patients with comparable illnesses in investor-owned hospitals.
C. Nonprofit hospitals do more fundraising than do investor-owned hospitals.
D. Doctors at nonprofit hospitals earn higher salaries than do similarly-qualified doctors at investor-owned hospitals.
E. Nonprofit hospitals receive more donations than do investor-owned hospital.

After analysis of the above statement, we can make it clear that the arguer want to establish the casual relationship between the listed factors, including less public investment in the form of tax breaks, fewer employees and higher occupancy levels, and a better way of delivering medical care.
How to undermine this reasoning?
In my view, I think that we can weaken this argument in two ways. On the one hand, we can destroy the casual relationship the arguer wants to create. On the one hand, we can cite the fact that opposite the conclusion the arguer want to come to.

So , taking into account the above analysis , B is sound.
Because B cites the fact opposing the conclusion.

A is out of scope. The statement does not mention the relationship between the number of per bed and the better way of delivering medical care.

C makes the same mistake. The relationship between the fundraising and the better way of delivering medical care.

D is repeating the above flaw. The reasoning that the higher salaries doctors received, the better way of delivering medical care is open to doubt.

Finally, E follows the same way again. The arguer fails to convince us that more donations will lead to the better way of delivering medical care.

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68. Since no one returns from death, we can never be certain about what passes through the mind of the dying person. For the unconscious, the confused, and the heavily sedated, these final moments are probably meaningless. However, for the mentally alert, it is quite possible that death presents itself as an unbelievably glorious experience, a flight into an entirely new universe of sensation. Why should we think so? Some people who have been reprieved from “certain” death at the last moment have experienced what goes through the consciousness of those who are not so fortunate. For example, parachutists who have survived falls report experiences that resemble psychedelic “trips”.

The primary point of the argument in the passage is

A. no one returns from death
B. dying can be a glorious experience
C. we can never know what passes through the mind of a dying person
D. some people are reprieved from death at the last moment
E. some people “die”, yet live to report their experiences

答案：B
思路：问题问短文论点。短文在第三行出现However，其前为一种现象的说法（不知道人死后思想上经历什么），其后强调另外一种死亡经历（Unbelievably glorious experience），后面说明后者的原因。故However引导的那句话是中心句。

A. 文中第一种说法，不正确。
B. 同However一句意思相同，正确。
C. 也是第一种说法，不正确。
D. 说明原因时使用的论据，非中心点。
E. 同D。

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101. Anson bases his conclusion about Dr. Ladlow on which one of the following?

A. an attack on Dr. Ladlow’s character
B. the application of a general principle
C. the use of an ambiguous term
D. the discrediting of facts
E. the rejectiion of a theoretical explanation


Questions 102-103
The brains of identical twins are genetically identical. When only one of a pair of identical twins is a schizophrenic, certain areas of the affected twin’s brain are smaller than corresponding areas in the brain of the unaffected twin. No such differences are found when neither twin is schizophrenic. Therefore, this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.

102. Which one of the following is an assumption required by the argument?

(A) The brain of a person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia.
(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.
(C) The brain of a person with an identical twin is no smaller, on average, than the brain of a person who is not a twin.
(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size.
(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.

答案：B
思路：
题干：assumption
原文：If one schizophrenic，then one smaller。If neither schizophrenic, then no difference. Conclusion: damage to physical structure cause schizophrenic
核心词：schizophrenic 注意：比较是在twin中进行的
我的习惯是从下到上地看选项。
E 无关项
D 原文没有的信息
C扩大了比较范围
A 扩大了比较范围
B ETS最爱：无他因

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103. If the statements on which the conclusion above is based are all true, each of the following could be true EXCEPT:

A. People who lack a genetic susceptibility for the disease will not develop schizophrenia
B. Medications can control most of the symptoms of schizophrenics share many of the characteristics found in those of people without the disorder
C. The brains of schizophrenics share many of the characteristics found in those of people without the disorder
D. It will eventually be possible to determine whether or not someone will develop schizophrenia on the basis of genetic information alone
E. Brain abnormalities associated with schizophrenia are the result of childhood viral infections that inhibit the development of brain cells

答案：C
题干： could be true, EXCEPT = must be false (按照老管的方法，找最确定的)
选项（从下到上）：
E 完全超出原文，不能判断
C完全超出原文，不能判断
B完全超出原文，不能判断
A超出原文，不能判断
D 注意文章第一句：“genetically identical”，选项最后一词“alone”。

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104. That the policy of nuclear deterrence has worked thus far is unquestionable. Since the end of the Second World War, the very fact that there were nuclear armaments in existence has kept major powers from using nuclear weapons, for fear of starting a worldwide nuclear exchange that would make the land of the power initiating it uninhabitable. The proof is that a third world war between superpowers has not happened.

Which one of the following, if true, indicates a flaw in the argument?

A. Maintaining a high level of nuclear armaments represents a significant drain on a country’s economy.
B. From what has happened in the past, it is impossible to infer with certainty what will happen in the future, so an accident could still trigger a third world war between superpowers.
C. Continuing to produce nuclear weapons beyond the minimum needed for deterrence increase the likelihood of a nuclear accident.
D. The major powers have engaged in many smaller-scale military operations since the end of the Second World War, while refraining from a nuclear confrontation.
E. It cannot be known whether it was nuclear deterrence that worked, or some other factor, such as a recognition of the economic value of remaining at peace.

答案：E
题干：flaw
原文：
Conclusion：policy worked.
Evidence: end of 2 world war ; 3 world war not happen.
casual explanation.
选项：从下到上
E 他因
D 事实陈述 可以作为weaken
C 无关项
B 迷惑项 请注意：原文是从已知的事实来推测导致事实的原因，所以该事实是不能被反对的。
A 无关项

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105. A survey of alumni of the class of 1960 at Aurora University yielded puzzling results. When asked to indicate their academic rank, half of the respondents reported that they were in the top quarter of the graduating class in 1960.

Which one of the following most helps account for apparent contradiction above?

A. A disproportionately large number of high ranking alumni responded to the survey.
B. Few, if any, respondents were mistaken about their class rank.
C. Not all the alumni who were actually in the top quarter responded to the survey.
D. Almost all of the alumni who graduated in 1960 responded to the survey.
E. Academic rank at Aurora University was based on a number of considerations in addition to average grades.

【正确答案】A
【解题思路】
本题的类型是解释类，即解释一个客观事实或现象发生的原因。
本题所陈述的客观事实是：参加调查的一半的对象（1960年的男校友）显示他们的成绩排名处于班上的前四分之一。
本题的考点是整体与部分之间的比例关系的逻辑思维。首先可以排除的是选项C和D，选项C说不是所有排名处于前四分之一的男校友参加了调查，选项D说几乎所有的1960年的男校友参加了调查，都更不利于解释已发生的事实，即使这个客观事实发生的可能性减少。选项E说学校的排名除了考虑平均成绩外，还考虑其他很多因素，但至少还是存在排名的，因此与发生的事实风牛马不相及。只有选项A说大量的不成比例的排名在前的男校友参加了调查最好地解释的所发生的客观事实， 选项B即使可能解释所发生的客观事实，也不如A选项为优。

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106. The seventeenth-century physicist Sir Isaac Newton is remembered chiefly for his treatises on motion and gravity. But Newton also conducted experiments secretly for many years abased on the arcane theories of alchemy, trying unsuccessfully to transmute common metals into gold and produce rejuvenating elixirs. If the alchemists of the seventeenth century had published the results of their experiments, chemistry in the eighteenth century would have been more advance than it actually was.

Which one of the following assumptions would allow the conclusion concerning eighteenth-century chemistry to be properly drawn?

A. Scientific progress is retarded by the reluctance of historians to acknowledge the failures of some of the great scientists.
B. Advances in science are hastened when reports of experiments, whether successful or not, are available for review by other scientists.
C. Newton’s work on motion and gravity would not have gained wide acceptance if the results of his work in alchemy had also been made public.
D. Increasing specialization within the sciences makes it difficult for scientists in one field to understand the principles of other fields.
E. The seventeenth-century alchemists could have achieved their goal only if their experiments had been subjected to public scrutiny.

【正确答案】B
【解题思路】
本题的类型是假设类，即所提出的假设是结论的一个必要条件。
本题的前提是：如果17世纪的炼金术士们公开他们的实验结果
本题的结论是：那么18世纪的化学将比其原来更为先进
前提中的核心词是：实验结果。结论中的核心词是：先进。要使某一假设成为该结论的必要条件，必然要提到实验结果与先进的关系，因此本题可用找核心词的办法进行快速排除，只有选项B包含这两个核心词。