托福指南上将推断题定义为检查考生对文章中强烈建议但绝不明说观点(strongly implied but not explicitly stated in the text) 的理解程度， 属于理解性题目。

由于“绝不明说”的题型设置方式，很多同学在解题的过程中会觉得摸不着头脑，感觉看哪儿都不对，但其实在遵循一审题、二定位、三推断基本解题方法的前提下，有些推断题根据逆向推理很快的就可以选出答案。今天我们就来讲一讲推断题当中逆向推理的三种情况：

一、直接对比推理

在这种情况下，会有两个事情的对比特征，问其中一个事物的特征，只要将与之形成对比的另外一个事情的特征否定掉就可以了， 例如TPO 2中的一个题目：

It should be obvious that cetaceans-whales， porpoises， and dolphins-are mammals. They breathe through lungs， not through gills， and give birth to live young. Their streamlined bodies， the absence of hind legs， and the presence of a fluke and blowhole can not disguise their affinities with land dwelling mammals. However， unlike the cases of sea otters and pinnipeds(seals， sea lions， and walruses， whose limbs are functional both on land and at sea) ， it is not easy to envision what the first whales looked like. Extinct but already fully marine cetaceans are known from the fossil record. How was the gap between a walking m ammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate， or transitional， between land mammals and cetaceans.

Which of the following can be inferred from paragraph 1 about early sea otters?

A. It is not difficult to imagine what they looked like

B. There were great numbers of them

C. They lived in these a only

D. They did not leave many fossil remains

根据审题，知晓题目中在问的是关于early sea otters”能推断出什么；回到原文中定位， 找到的解题关键句是“However，unlike the cases of· the first whales look like'”这句话中将sea otters and pinnipeds和whales进行对比， 说不像前两者， 要去想象后者是什么样子是不容易的；再来对比选项，根据解题句的说法，选项A就是显而易见的答案了。

识别直接对比的常见信号单词有：unlike， in contrary，contrast with， differ from等。

二、时间对比推理

这种情况和直接对比推理相似，换汤不换药，只不过是把两个事物换成了两段时间，它们所具有的特征一般相反，当题目问一个时间段的特征时，只要将与之相反的时间段的特征否定掉就可以了。当然识别时间对比推理的信号单词肯定也换成了和时间相关的表达， 比如说before， after， prior to等， 具体例题，同学们可参考TPO 20， Westward Migration中的题。

三、集合概念推理

在这种情况下，一个大的集合的两个方面形成对比，两者之间存在着互补性关系，部分构成整体，整体决定部分。但是单纯的部分和整体的概念过于简单粗暴，真题中将这种情进行了变形，依托于举例逻辑将它进行了难度升级，具体是怎么样的情况呢， 我们来看TPO 3当中的一个题：

Even the kind of stability defined as simple lack of change is not always associated with maximum diversity. At least intemperate zones， maximum diversity is often found in mid-successional stages，not in the climax community. Once a redwood forest matures， for example， the kinds of species and the number of individuals growing on the forest floor are reduced. In general， diversity， by itself， does not ensure stability y. Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite， in fact. A more complicated system is， in general， more likely thana simple system to breakdown. A fifteen-speed racing bicycle is more likely to breakdown than a child's tricycle.

Which of the following can be inferred from paragraph 5 about redwood forests?

A.     They become less stable as they mature

B.     They support many species when they reach climax

C.     They are found intemperate zones

D.    They have reduced diversity during mid-successional stages

根据审题， 知晓题目中在问的是关于“redwood forests”能推断出什么； 回到原文中定位， 找到的解题关键句是“Once a redwood forest matures…are reduced”，这句话中非常明显是个例子，例子的存在是为了解释说明观点句，举例逻辑的重点应该是在观点句上，那么这个例子之前的句子讲到的是：至少在温带地区，会经常在演替的过程中发现最多的物种，而不是在群落中；再来对比选项，这道题的答案就应该是选项C。很多同学这个时候可能会一头雾水，为什么答案是这个，不用想的太复杂，就是因为举例逻辑中的观点句和例子也构成了整体和部分的关系。这种情况， 同学们还可以参考TPO 38， Transgenic Plants中的第四题。

牢记每种情况的信号单词，勤加练习，及时总结，考试中遇到逆向推理的情况时，相信同学们一定可以手到擒来!

新航道重庆学校官网：cq.xhd.cn

新航道重庆学校电话：400-185-9090