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91. Leachate is a solution, frequently highly contaminated, that develops when water permeates a landifill’s site. If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment, generally in unpredictable quantities. A method must be found for disposing of leach ate. Most landfill leachate is sent directly to sewage treatment plants, but not all sewage plants are capable of handling the highly contaminated water.
Which one of the following can be inferred from the passage?
A. The ability to predict the volume of escaping landfill leachate would help solve the disposal problem.
B. If any water permeates a landfill, leachate will escape into the environment.
C. No sewage treatment plants are capable of handling leachate.
D. Some landfill leachate is sent to sewage treatment plants that are incapable of handling it.
E. If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.
此题为充要条件的逆否命题。
A是B的充要条件，那末他的逆否命题比正确! 非B推出非A
If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment, ---------〉If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.
参考答案E
思路：原文说：“Leachate(浸析液)是一种水渗透过垃圾填埋地后生成的溶液，这种溶液通常是高度污染的。当且仅当超出垃圾填埋的容水能力时(A)，Leachate会泄露到外界环境中(B)。必须找到一种处理L的方法。许多L被送去用于污水灌溉，但不是所有的污水灌溉的植物都有能力处理这种被高度污染的水”。
原文中If and only if A then B(从B可推出A);选项E为If not A then not B(非A推非B)正确
A. 原文没有说
B. 条件不对
C. 原文是一部分plants没有这种能力
D. 原文只说明并非所有的污水灌溉的植物都有能力处理这种被高度污染的水，没说some Leachate一定是被送去浇那些无此能力的植物。
92. Baking for winter holidays is a tradition that may have a sound medical basis. In midwinter, when days are short, many people suffer from a specific type of seasonal depression caused by lack of sunlight. Carbohydrates, both sugars and starches, boost the brain’s levels of serotonin, a neurotransmitter that improves the mood. In this respect, carbohydrates act on the brain in the same way as some antidepressants. Thus, eating holiday cookies may provide an effective form of self-prescribed medication.
Which one of the following can be properly inferred from the passage?
A.Seasonal depression is one of the most easily treated forms of depression.
B.Lack of sunlight lowers the level of serotonin in the brain.
C.People are more likely to be depressed in midwinter than at other times of the year.
D.Some antidepressants act by changing the brain’s level of serotonin.
E.Raising the level of neurotransmitters in the brain effectively relieves depression.
从这句话, boost the brain’levels of serotonin, a neurotransmitter that improves the mood, 得知, 只是serotonin有抗忧郁的作用, 而不是所有的neurotransmitter.
D is correct.
A，most easily treated forms和原文无关
B，没有提到的无关信息
C，无关比较
E，把原文的信息扩大范围了，原文说的是a neurotransmitter， E中变成了所有neurotransmitters。
93. The efficiency of microwave ovens in destroying the harmful bacteria frequently found in common foods is diminished by the presence of salt in the food being cooked. When heated in a microwave oven, the interior of unsalted food reaches temperatures high enough to kill bacteria that cause food poisoning, but the interior of salted food does not. Scientists theorize that salt effectively blocks the microwaves from heating the interior.
Which one of the following conclusions is most supported by the information above?
A.The kinds of bacteria that cause food poisoning are more likely to be found on the exterior of food than in the interior of food.
B.The incidence of serious food poisoning would be significantly reduced if microwave ovens were not used by consumers to cook or reheat food.
C.The addition of salt to food that has been cooked or reheated in a microwave oven can increase the danger of food poisoning.
D.The danger of food poisoning can be lessened if salt is not used to prepare foods that are to be cooked in a microwave oven.
E.Salt is the primary cause of food poisoning resulting from food that is heated in microwave ovens.
In my view, the reasoning in this argument is that:
On the one hand:
the presence of salt in the food being cooked? salt effectively blocks the microwaves from heating the interior? The efficiency of microwave ovens in destroying the harmful bacteria frequently found in common foods is diminished
On the other hand:
unsalted food is heated by microwave? the interior of unsalted food reaches temperatures high enough? kill bacteria that cause food poisoning
So , D is the best choice.
A.is out of scope because the exterior of food is not mentioned in this argument.
B.is also out of scope too. We never know what will happen if microwave ovens were not used by consumers to cook or reheat food. Because the statement have no the relevant information.
C.is puzzle. The statement just infers that the harmful bacteria frequently found in common foods is keep same. The salt only prevent microwave from destroying such bacteria. Even though the addition of salt to food will significantly prevent the efficiency of microwave ovens, we can not reach the conclusion that the addition of salt to food that has been cooked or reheated in a microwave oven can increase the danger of food poisoning. So C is problematic choice.
D.is the best choice.
E.may be the extreme pole. The statement not mention that salt is the primary cause of food poisoning resulting from food. It is possible that salt is the relevant factor in determining the efficiency of microwave ovens.
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 ? 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.
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.? 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.