解答推理题应从识别题型入手。推理题题干中常见表示推理或暗示的词汇：infer，imply，indicate，suggest。然后，仔细阅读题干。最后，根据题干信息研读文章信息以做出推理。
接下来我们通过一些例题来深入解析推理题中对比取反的情况。
1. Paragraph: Two other developments presaged the end of the era of turnpikes and started a transportation revolution that resulted in increased regional specialization and the growth of a national market economy. First came the steamboat; although flatboats and keelboats continued to be important until the 1850s, steamboats eventually superseded all other craft in the carrying of passengers and freight. Steamboats were not only faster but also transported upriver freight for about one tenth of what it had previously cost on hand-propelled keelboats.
1. Which of the following can be inferred from the paragraph about flatboats and keelboats?
A. They ceased to be used as soon as the first turnpikes were built.
B. They were slower and more expensive to operate than steamboats.
C. They were used for long-distance but not for regional transportation.
D. They were used primarily on the Erie Canal.
根据题干信息flatboats and keelboats对应到原文句子Steamboats were not only faster but also transported upriver freight for about one tenth of what it had previously cost on hand-propelled keelboats. 从句子里steamboat以及keelboats之间的faster 以及one tenth of很容易得出B选项。解出答案之后，希望大家思考，这样一道推理题透露了出题人设置题目时的逻辑思维，那就是信息的对比，而且有对比的时候，答案往往会取反面。
2. Paragraph: A symbiotic relationship is an interaction between two or more species in which one species lives in or on another species. There are three main types of symbiotic relationships: parasitism, commensalism, and mutualism. The first and the third can be key factors in the structure of a biological community – that is, all the populations of organisms living together and potentially interacting in a particular area.
1. Which of the following statements about commensalism can be inferred from the paragraph?
A. It excludes interactions between more than two species.
B. It makes it less likely for species within a community to survive.
C. Its significance to the organization of biological communities is small.
D. Its role in the structure of biological populations is a disruptive one.
根据题干信息commensalism对应到原文句子There are three main types of symbiotic relationships: parasitism, commensalism, and mutualism.该句得不出答案，接着看到The first and the third can be key factors in the structure of a biological community;该句告诉我们first and third指代上句中的parasitism和mutualism, 而题干中被问及的commensalism(共栖)恰是三者之中剩余的部分，根据例一中出题人对于对比取反的逻辑设置，显然该题同样取反，既然文中给出一三重要，那么强烈暗示的就是处于第二的commensalism不重要，所以选C。
3. Paragraph: Isotopic analysis of shells allowed geologists to measure another glacial effect. They could trace the growth and shrinkage of continental glaciers, even in parts of the ocean where there may have been no great change in temperature – around the equator, for example. The oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice. During glaciations, the lighter oxygen-16 has a greater tendency to evaporate from the ocean surface than the heavier oxygen-18 does. Thus, more of the heavy isotope is left behind in the ocean and absorbed by marine organisms. From this analysis of marine sediments, geologists have learned that there were many shorter, more regular cycles of glaciation and de-glaciation than geologists had recognized from the glacial drift of the continents alone.
1. It can be inferred from paragraph 5 that foraminifera fossil shells containing calcite with high percentages of oxygen-16 were deposited at times when…
A. polar ice extended as far as equatorial regions of land and sea.
B. extensive glaciation was not occurring.
C. there were no great increases in ocean temperature.
D. there was heavy snowfall on continental glaciers.
同样根据题干信息oxygen-16对应到原文During glaciations, the lighter oxygen-16 has a greater tendency to evaporate from the ocean surface than the heavier oxygen-18 does. 句中给出during glaciations的时候oxygen-16会蒸发离开，题干问什么时候oxygen-16 were deposited, 同样还是对比取反，即not during glaciations，对应选项B。
4. Paragraph 2: The areas covered by this material were so vast that the ice that deposited it must have been a continental glacier larger than Greenland or Antarctica. Eventually, Agassiz and others convinced geologists and the general public that a great continental glaciation had extended the polar ice caps far into regions that now enjoy temperate climates. For the first time, people began to talk about ice ages. It was also apparent that the glaciation occurred in the relatively recent past because the drift was soft, like freshly deposited sediment. We now know the age of the glaciation accurately from radiometric dating of the carbon-14 in logs buried in the drift. The drift of the last glaciation was deposited during one of the most recent epochs of geologic time, the Pleistocene, which lasted from 1.8 million to 10,000 years ago. Along the east coast of the United States, the southernmost advance of this ice is recorded by the enormous sand and drift deposits of the terminal moraines that form Long Island and Cape Cod.
1. It can be inferred from paragraph 2 that Agassiz and other geologists of his time were not able to determine…
A. which geographic regions had been covered with ice sheets in the last ice age.
B. the exact dates at which drifts had been deposited during the last ice age.
C. the exact composition of the drifts laid during the last ice age.
D. how far south along the east coast of the United States the ice had advanced during the last ice age.
通过以上的例子，相信大家已经熟悉了推理题中对比取反的逻辑思维。那么最后这一道题，是否能够应用讲解的规律顺利得出正确答案呢?
首先读题干，很多考生会选择Agassiz and other geologists这一信息去对应原文，结果发现无法根据文中对应信息得出正确答案。此时要牢记对比取反的逻辑思维，重新审题发现了of his time这一时间短语与文中的We now know the age of the glaciation accurately from radiometric dating of the carbon-14 in logs buried in the drift.一句里的now构成对比关系。所以根据对比取反的逻辑，既然我们现在才精确知道冰川形成的时间，那么在当时是不知道的，顺利选出B选项。