推断题Inference Question，又叫推理题，是许多同学最烦恼的阅读题型。往往阅读已达25分以上的同学，最后的几道错题中就有推断题的身影。曾遇到一个分数已经29的高分学员，二刷托福的最后阶段，还是每每在推断题上栽跟头。

　　原因呢，就在于推断题逻辑的“模糊”——比起大部分题型，比如细节题简单粗暴、非黑即白的逻辑，推断题的态度要显得暧昧许多。但首先我们要确定的是，虽然很难在原文中找到直接的同义改写，但文中一定会有依据。一旦依据不足，那做的就不是推断题，而是“脑补题“了。问我们：“What can we infer about XXX”，实际上是问“作者对XXX有什么潜台词?”

　　潜台词里套路多，所以我们首先把题目分为两类。一类是(1)“题干定位“型，一类可以叫作(2)“选项定位型“。读完题干就可以区分。举个简单的例子：

　　现在城市中养猫的人群正在兴起，逐渐改变了以往狗多猫少的情况。其中原因有很多，首先，比起养狗，养猫更加方便。猫咪几乎没有体味，不需要遛，也不需要经常洗澡：猫会自己“洗澡”。与狗不同，它们的唾液有很强的清洁力。此外，猫比狗需求的陪伴更少，这很适合生活忙碌的白领人群。现代宠物行业培养了许多适宜家养的猫咪品种。比如美国短毛猫，脾气较为温顺，尤其是银虎斑，性格乖巧，适合作为家养宠物。

　　根据这段原文出两道推断题。(1)关于美国短毛猫，我们可以推断出什么结论?(2)关于养猫，我们可以推断出什么结论?那么第一题就是“题干定位题”，因为“美国短毛猫”可以确定定位区间——原文的最后一句话。而第二题，我们却显然无法根据题干来定位，因为整段文字都是讲养猫的。所以第二题我们采取的策略是根据选项去定位。我们可以叫它“选项定位型”。

　　区分了两种类型，就可以分别看看它们的套路了!

　　一个简单的思维导图：

　　今天我们要详细讲解的是题干定位型的推断题。以下是一些用得上的推理逻辑。

　　1. 反向推理

　　要有信心的是：只要题干中的关键词是可以定位的，这道题就肯定不难，肯定可以拿下。我们要做的就是紧扣定位区间，从几句话中确定依据，再回头看选项。很快就可以知道哪几个选项的依据不足。我们还是根据上面这个养猫的例子来出几道题，考考大家的逻辑。

　　1. 关于动物的唾液，我们能推断出什么结论?

　　A. 猫的唾液比人类的沐浴液更有清洁力。

　　B. 狗的唾液没有清洁力。

　　C. 动物的唾液都有清洁力。

　　D. 因为猫的唾液可以自我清洁，所以猫的一生不需要洗澡。

　　这道题拿到手，当然是用“唾液“作为关键词去定位。找到定位区间：“猫咪并不需要遛，也不需要经常洗澡：猫会自己“洗澡”。与狗不同，它们的唾液有很强的清洁力。“依据仅有这两句话，其中没有提到“人类的沐浴液”，因此排除A;“猫不需要经常洗澡”和D中的“一生不需要洗澡”矛盾，排除D;C显然不对，因此选择B。

　　B这个选项，我们叫做反向推理，由“与狗不同，……”这句话推出。这个逻辑非常常见。现在来看一看TPO中的练习题：

　　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 cannot 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 mammal 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 the sea only.

　　D. They did not leave many fossil remains.

　　这道题是非常经典的题干定位、反向推理。题干中的sea otter, 定位到的区间为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.逻辑和上面那道例题非常相似，根据unlike推出sea otter情况与cetacean相反，因此选A。

　　还有一种更为隐晦的反向推理。比如，托福出分了，妈妈对你说：你和小明、小红都是一个班的，你看看小明这次考得特别好，小红也考得不错!请问根据妈妈的话可以推断出什么?当然是妈妈的潜台词：“你”没有考好。这件事妈妈没有明说，但仍然是反向推理出来的。

　　那就让我们把这种题目拿下，考出个超级好的成绩，让妈妈无话可说：

　　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.

　　Which of the following statements about commensalism can be inferred from paragraph 1?

　　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.

　　根据题干的commensalism, 找到定位区间“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”。第一句话罗列了三种关系，第二句话强调了第一种和第三种是key factor，那么没有提到的第二种——也就是题干所问的这一种，就是与之相反的不是key factor。答案呼之欲出：就是C,its significance is small.

　　再来一题更难的：

　　With question such as these clearly before them, the scientists aboard the Glomar Challenger processed to the Mediterranean to search for the answers. On August 23, 1970, they recovered a sample. The sample consisted of pebbles of hardened sediment that had once been soft, deep-sea mud, as well as granules of gypsum and fragments of volcanic rock. Not a single pebble was found that might have indicated that the pebbles came from the nearby continent. In the days following, samples of solid gypsum were repeatedly brought on deck as drilling operations penetrated the seafloor. Furthermore, the gypsum was found to possess peculiarities of composition and structure that suggested it had formed on desert flats. Sediment above and below the gypsum layer contained tiny marine fossils, indicating open-ocean conditions. As they drilled into the central and deepest part of the Mediterranean basin, the scientists took solid, shiny, crystalline salt from the core barrel. Interbedded with the salt were thin layers of what appeared to be windblown silt.

　　Which of the following can be inferred from paragraph 3 about the solid gypsum layer?

　　A. It did not contain any marine fossil.

　　B. It had formed in open-ocean conditions.

　　C. It had once been soft, deep-sea mud.

　　D. It contained sediment from nearby deserts.

　　这题拿到手，还是找定位区间：“the gypsum was found to possess peculiarities of composition and structure that suggested it had formed on desert flats. Sediment above and below the gypsum layer contained tiny marine fossils, indicating open-ocean conditions.”第一句话说gypsum的内在结构说明它是在沙漠形成的;第二句话讲了gypsum上下两层的情况：富含marine fossils。从第二句话中，我们倾向于推出中间的gypsum曾并没有marine fossils，逻辑和上题一样。第一句话给了我们佐证：gypsum本身应当从沙漠来，当然没有海洋沉淀。答案：A。

　　反向推理的逻辑大致如此。其中还有一种较为特殊的“时间推理”，我们也可以看一看。

　　2. 时间推理

　　时间推理的逻辑非常简单。大致就是：小明在2017年去了美国读大学——可以推出2017年以前小明没有去美国读大学。通过时间先后来反推，其实也属于反向推理中的一种。一道简单的TPO：

　　The story of the westward movement of population in the United States is, in the main, the story of the expansion of American agriculture—of the development of new areas for the raising of livestock and the cultivation of wheat, corn, tobacco, and cotton. After 1815 improved transportation enabled more and more western farmers to escape a self-sufficient way of life and enter a national market economy. During periods when commodity prices were high, the rate of westward migration increased spectacularly.

　　What can be inferred from paragraph 1 about western farmers prior to 1815?

　　A. They had limited their crop production to wheat, corn, tobacco,

　　and cotton.

　　B. They were able to sell their product

　　at high prices.

　　C. They had not been successful in raising cattle.

　　D. They did not operate in a national market economy.

　　答案选C。你选对了吗?

　　再来看一看时间推理更进一步的题会出成什么样：

　　This was before the steam locomotive, and canal building was at its height. The companies building the canals to transport coal needed surveyors to help them find the coal deposits worth mining as well as to determine the best courses for the canals. This job gave Smith an opportunity to study the fresh rock outcrops created by the newly dug canal. He later worked on similar jobs across the length and breadth of England all the while studying the newly revealed strata and collecting all the fossils he could find. Smith used mail coaches to travel as much as 10000 miles per year. In 1815 he published the first modern geological map “A Map of the Strata of England and Wales with a Part of Scotland”, map so meticulously researched that it can still be used today.

　　Which of the following can be inferred from paragraph 2 about canal building?

　　A. Canals were built primarily in the south of England rather than in other regions.

　　B. Canal building decreased after the steam locomotive was invented.

　　C. Canal building made it difficult to study rock strata which often became damaged in the process.

　　D. Canal builders hired surveyors like Smith to examine exposed rock strata.

　　这道题目跪了无数人。其实这题看似信息杂乱，但题目中的canal building是可以定位的：文中的前3句话。第一句话就是题眼所在：在steam locomotive出现之前，canal building was at its height。你是否理解了at its height?它表示“达到了顶峰“。所以简单地画一个图，是这样的：

　　所以选B，毫无疑问。A信息不足，而C和D都和原文有不同程度的出入。