GMAT逻辑题实例讲解，首先普通逻辑题目篇：
例题：Which of the following most logically completes the passage?
Using new detection techniques, researchers have found trace amounts of various medicinal substances in lakes and rivers. Taken in large quantities, these substances could have serious health effects, but they are present in quantities far too low to cause any physiological response in people who drink the water or bathe in it. Nevertheless, medical experts contend that eliminating these trace amounts from the water will have public health benefits, since __________.
(A). some of the medicinal substances found in lakes and rivers are harmless to humans even if taken in large quantities
(B). some of the medicinal substances found in lakes and rivers can counteract possible harmful effects of other such substances found there
(C). people who develop undesirable side effects when being treated with medicines that contain these substances generally have their treatment changed
(D). most medicinal substances that reach lakes or rivers rapidly break down into harmless substances
(E). disease-causing bacteria exposed to low concentrations of certain medicinal substances can become resistant to them
这道题如果运用正常的逻辑思维去想，恐怕要花费5-6分钟了。为了节约GMAT 的宝贵时间，我们运用重心重合论去解决。原文主要表达微量的药用物质对于健康有害。那么在ABCDE几个选项中找一个符合原文说法的就OK了。A 很明显错了，harmless 一词已经暗示了足够的信息，和原文不符。B counteract 是抵消，好的意思。也和原文表达的不符。C 治疗方式改变的问题，和原文没有任何关系，排除。D 物质分解成无害的物质，harmless，和A 选项错误类型相同。排除 E 引起疾病的病毒在遇到低含量的药用物质时会产生抗药性。这就说明这种药用物质的确是有害的，完全符合原文意思，因此是正确答案。
偏题怪题篇：
A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.
The conclusion above is not properly drawn unless which of the following is true?
(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents.
(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.
(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.
这道题号称历年GMAT 最难题。其实很好做。原文谈到80%，和它关系最密切的就是20%。答案就是A。
上述就是两个典型GMAT逻辑题实例讲解，综上两个例子，不难看出，答案的选择永远是来源于原文，从原文中找答案才是最为重要的一点。
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