Part 2 逻辑题的解题方法

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在新GRE考试的每一个语文section中，都存在一篇阅读文章，文章词数很少，200词以内，只出一道题，位置通常在第16或第17题，被我们称为逻辑单题。这种题目的解题思路和其他阅读题型完全不同，所以值得我们单独拿出一章来讨论其方法。逻辑题型种类非常多，到目前为止，GRE官方提供的逻辑题型加上考场上实际出现过的逻辑题型多达十二种，分别为黑体字题（Boldface）、归纳题（lnference）、矛盾题（Contradiction）、解释题（Explanation）、削弱题（Weaken）、假设题（Assumption）、充分假设题（Sufficient Assumption）、加强题（Strengthen）、评价题（Evaluation）、填空题（Logical Completion）、定义题（Definition）、论证概括题（Generalization），且每种题型的解题思路都不尽相同。当然，并不是每种题型都在考场上频繁出现，其中很多种，比如Generalization，Evaluation和Definition很少出现，而Contradiction只在官方指南上出现过。所以，本章节将主要探讨经常遇到的、有系统性解题思路的几种题型：Boldface，lnference，Weaken，Assumption，Strengthen，以及Logical Completion。

基础知识

在逻辑单题中，不同题型分别考查我们理解（Understand）、构造（Construct）、评论（Evaluate）一个Argument的能力。由于各题型的考查目的不同，且一篇文章只出一道题，建议大家先看题干考查什么，再去看文章。

什么是Argument？

Argument在逻辑学中的定义是：a set of statements in which one of the statements is supported by the others，即所谓的论证指的是一组语句所组成的集合，其中一个语句被其他语句所支持。其中，被支持的语句被称为Conclusion，即结论；而用来支持结论的语句被称为Premise（s），即前提。根据定义，论证中最重要的关系是Support（支持）关系。

在考试中，有些题型考查我们理解论证，即别人给出一篇论证，我们要去理解它在用哪些前提支持哪个结论；有些题型考查我们制造论证，即给出已知条件，我们来推出合适的结论；有些题型考查我们评价论证，即给出论证，让我们评价这个论证的合理性。

不知道同学们是否选对了，以上属于论证的是（3）和（4）。（1）不是论证，因为根本就没有多个命题之间的关系，而论证必须涉及命题关系。（2）是很多同学会判断错误的例子——许多人觉得标志结论的字眼应该是“所以”，所以只要句子中有“所以”连接前后两个命题的关系，就似乎一定是论证。

这个想法是片面的，“所以”或“so”“therefore”这样的词表达两种可能的关系：一是先发生的事情与后发生的事情两个事实之间的因果关系[如（2）]，指的是前者导致了后者，并没有支持某一个观点，这不是论证。“所以”的另一种作用，即在论证中的作用，是表达推断关系，由已知的前提推断未知的结论。已知和未知的命题之间没有必然的先后顺序，我们有时候先知道后发生的事情，推测先前导致它的原因；有时候先知道先发生的事情，推测其可能导致的结果；有时候先知道的事情和所推断的事情之间根本就没有因果关系。同学们在判断论证的时候，关键是要寻找结论，而结论必然是一个未知的判断，所以，最可靠的标志不是诸如“因此”“所以”之类的字眼，因为它们有多重含义；而是表达“推断”的字眼，比如：“一定”“肯定”“显然”等，对应到英文中，经常就是“must”“should”“clearly”“obviously”“likely”等。当然，如果有多个这种词出现，很可能是作者先做了一个判断，再去做进一步的判断，我们需要关注它们之间的关系，看清楚是由哪个命题推出哪个命题。

一、黑体字功能题（Boldface）

方法论

这种题型考查的是理解一个论证的能力。通常会呈现一篇短文，并在文章中用黑体字标出两个片段，问这两个片段在文章中所起的作用。在解这种题型时，同学们需要注意，我们就是在找前提和结论。当然，一篇文章有可能包含多组论证，意味着包含多个观点，有的是陈述者自己的观点，有的是他所反对的观点，所以我们还需要随时弄清楚所看到的语句与作者立场之间的同反关系。偶尔，作者会对对立的观点做出妥协，因此偶尔有的语句的功能是表让步的。

这意味着，在这种题目中我们最需关注的不是体现文章具体所说事件的词语，而是能够体现前提结论关系（therefore，the reason is that，can be supported by，since…）的字眼，以及能够体现不同视角的字眼。

基于以上对我们可能读到的短文的分析，我们会期望选项能够传达的信息是：语句体现的立场（作者的立场或作者立场的对立面）、语句在论证中的作用（前提或证据、观点或结论）。当然，我们需要防范让步信息的出现。

在做这种题型时，阅读速度没有必要很慢。我们并不需要读懂文章的内容，而要看懂文章信息片段之间的逻辑关系词。

[例1]

Last year a record number of new manufacturing jobs were created. Will this year bring another record? Well，a new manufacturing job is created either within an existing company or by the start-up of a new company. Within existing firms，new jobs have been created this year at well below last year's record pace. At the same time，there is considerable evidence that the number of new companies starting up will be no higher this year than it was last year，and surely the new companies starting up this year will create no more jobs per company than did last year's start-ups. Clearly，it can be concluded that the number of new jobs created this year will fall short of last year's record.

In the argument given，the two portions in boldface play which of the following roles?

（A）The first is a prediction that，if accurate，would provide support for the main conclusion of the argument；the second is that main conclusion.

（B）The first is a prediction that，if accurate，would provide support for the main conclusion of the argument；the second is a conclusion drawn in order to support that main conclusion.

（C）The first is an objection that the argument rejects；the second is the main conclusion of the argument.

（D）The first is an objection that the argument rejects；the second presents a conclusion that could be drawn if that objection were allowed to stand.

（E）The first is a claim that has been advanced in support of a position that the argument opposes；the second is a claim advanced in support of the main conclusion of the argument.

解析：两处黑体字之间的“Clearly，it can be concluded”体现了前者是在支持后者。且两处黑体字的视角都是作者的视角。所以很明显答案是A。

B错在后半句，第二句话本身就是最终结论。

C错在前半句，本文一直是一个人的视角，没有去反驳（object）任何东西。

D与C错误同样。

E与C、D错误同样，不存在反驳（oppose）。

正确选项：A。

[例2]

In countries where automobile insurance includes compensation for whiplash injuries sustained in automobile accidents，reports of having suffered such injuries are twice as frequent as they are in countries where whiplash is not covered. Presently，no objective test for whiplash exists，so it is true that spurious reports of whiplash injuries cannot be readily identified. Nevertheless，these facts do not warrant the conclusion drawn by some commentators that in the countries with the higher rates of reported whiplash injuries，half of the reported cases are spurious. Clearly，in countries where automobile insurance does not include compensation for whiplash，people often have little incentive to report whiplash injuries that they actually have suffered.

In the argument given，the two boldfaced portions play which of the following roles?

（A）The first is a claim that the argument disputes；the second is a conclusion that has been based on that claim.

（B）The first is a claim that has been used to support a conclusion that the argument accepts；the second is that conclusion.

（C）The first is evidence that has been used to support a conclusion for which the argument provides further evidence；the second is the main conclusion of the argument.

（D）The first is a finding whose implications are at issue in the argument；the second is a claim presented in order to argue against deriving certain implications from that finding.

（E）The first is a finding whose accuracy is evaluated in the argument；the second is evidence presented to establish that the finding is accurate.

解析：第一处黑体字之后的so it is true that体现黑体字是前提，用来支持so it is true that之后的结论，我们暂时称之为P。但是后面的“Nevertheless，these facts do not warrant the conclusion drawn by some commentators that”体现，刚才这些结论P被某些commentators用来推断出新的结论Q，而且Q是作者反对的。那么作者理应对自己的反驳进行辩护，于是尽管接下来是“Clearly”，但之后的第二处黑体字作者必须提供理由。所以选D。

A的前半句已经错了，作者要dispute的不是第一处黑体字本身。

B的前半句也错了，作者没有accept第一处黑体字所推出的结论。

C的前半句也错了，第一处黑体字所推出的结论作者并不会给更多证据支持。

E的前半句也错了，第一处黑体字本身是事实，不会去evaluate。

正确选项：D。

二、归纳题（Inference）

方法论

由以上问法可以看出，这种题型是在考查制造一个论证的能力。基于原文信息，我们要判定哪个结论可以推断出。这种考法决定了这种题型是技巧性最差的题型之一，因为它没有任何逻辑上的弯路，是顺着原文进行思考。原则上，一切按照逻辑学公理、定理体系能够进行的严密推理都是必须要掌握的，但同学们现在不可能学习整个逻辑学，因为没有时间；同时，我们也没这个必要，因为每个人日常都会有一定的逻辑直觉。这种题型的最大要义是：不要引入额外的背景知识。

比如：万炜很努力，而万炜考上了北大。问：能否推断出“万炜的努力让他考上了北大”？答：不能，两件事情的伴随发生不意味着有因果关系。

再比如：万炜一直不努力，所以他成绩非常不好。问：能否推断出“如果万炜努力，他成绩就能提高”？答：不能，A导致了B不代表～A就会导致～B。简单来说，就是我们必须做到逻辑严谨，不引入额外条件。

[例]

People tend to estimate the likelihood of an event's occurrence according to its salience；that is，according to how strongly and how often it comes to their attention. By placement and headlines，newspapers emphasize stories about local crime over stories about crime elsewhere and about many other major events.

It can be concluded on the basis of the statements above，if they are true，which of the following is most probably also true?

（A）The language used in newspaper headlines about local crime is inflammatory and fails to respect the rights of suspects.

（B）The coverage of international events in newspapers is neglected in favor of the coverage of local events.

（C）Readers of local news in newspapers tend to overestimate the amount of crime in their own localities relative to the amount of crime in other places.

（D）None of the events concerning other people that are reported in newspapers is so salient in people's minds as their own personal experiences.

（E）The press is the news medium that focuses people's attention most strongly on local crimes.

思考过程：

题干的核心信息是：（1）人们靠信息位置的醒目来判定事件发生的可能性；（2）当地犯罪新闻处在头条的位置，而外地犯罪新闻不在头条的位置，头条更醒目。显然，结论自然就是：人们会更容易觉得当地犯罪的可能性比外地犯罪的可能性高。

正确选项：C。

三、解释题（Explanation）

方法论

这种题型仍然是在考查我们制造论证的能力。只不过，与归纳题不同的是，归纳题需要我们得出绝对严谨的结论，而解释题只是让我们提出一种可能的解释。解释题一般出在一件怪事之后，要求考生寻找一个选项可以最好地解释文章中的怪事。题干有可能提示我们具体要解释的现象，但即便题干没有提示，我们一般也能很容易判断到底需要解释什么。

我们的目的是在满足原文所有事实的背景下，找一个可能的选项，使得原文的怪事看起来不再奇怪。阅读的重点在于，文章中通常会有一个转折来体现意料之外的事情，我们要努力找到这个令人奇怪的事情，并从答案中选择其解释。请注意，所谓寻找一个“解释”来解释某事，就是寻找一个事件成为导致某事的原因，而不是证明某事的证据。比如，万炜非常努力，但就是考不好。什么可以解释呢？万炜脑子特别笨，这可以解释，因为脑子笨可以导致努力了也考不好。但是，万炜100分的卷子只答了30分，这就不行。因为100分的卷子只答了30分不能导致他考不好，这是考不好的证据，是考不好这件事情更具体的表现。

[例]

Parland's alligator population has been declining in recent years，primarily because of hunting. Alligators prey heavily on a species of freshwater fish that is highly valued as food by Parlanders，who had hoped that the decline in the alligator population would lead to an increase in the numbers of these fish available for human consumption. Yet the population of this fish species has also declined，even though the annual number caught for human consumption has not increased.

Which of the following，if true，most helps to explain the decline in the population of the fish species?

（A）The decline in the alligator population has meant that fishers can work in some parts of lakes and rivers that were formerly too dangerous.

（B）Over the last few years，Parland's commercial fishing enterprises have increased the number of fishing boats they use.

（C）The main predator of these fish is another species of fish on which alligators also prey.

（D）Many Parlanders who hunt alligators do so because of the high market price of alligator skins，not because of the threat alligators pose to the fish population.

（E）ln several neighboring countries through which Parland's rivers also flow，alligators are at risk of extinction as a result of extensive hunting.

解析：文章中的悖论是：明明fish的天敌alligators变少了，并且捕鱼的人也没有捕更多的鱼，那么理应鱼多了，但鱼却少了。所以，我们要寻找一个可以导致鱼变少的可能性。答案选C，因为alligators捕捉鱼的主要天敌alligators少了，鱼的天敌就多了，就可以导致鱼变少。

正确选项：C。

四、削弱题（Weaken）

接下来进入的一系列的题型是整个逻辑体系中最难的题型，因为它们都是在考查我们评价论证的能力（削弱、加强等）。要想评价别人的论证，必须首先理解别人的论证，所谓理解，我们必须要区分别人论证的逻辑类型。

人类的Argument类型数不胜数，但是GRE考试中最常见的是以下三种，大家必须熟练辨识。

1 结果型论证，即已知某事件，推断其曾经导致或将导致的结果。如：

万炜很努力，所以他一定能考好。

万炜长得很丑，所以他一定找不到对象。

万炜很懒惰，所以他后来肯定没考好。

2 解释型论证，即已知某事件，推断导致它的原因。解释型论证有多种表现形式，如：

万炜这次没考好。显然，他之前没努力。

万炜之前没努力，后来他就没考好。显然，是因为他没努力导致了他没考好。

万炜没考好。显然，是因为他没努力造成了这一结果。

朝南的房子价钱相对更贵。显然，人们喜欢阳光充足的地方。

技巧：在理解文章逻辑的过程中，我们会尝试建立一条完整的因果链（如果存在），比如，没努力→没考好；南→阳光充足→房价高。只要结果是已知事实，那么该论证一定是解释型论证。

3 类比型论证，即在相似对象间进行属性类推。如：

万炜上次考试没努力后来考砸了。显然，如果这次他不努力肯定还会考砸。

苹果很受欢迎，因为富含维C。所以，同样富含维C的橙子肯定也受欢迎。

这种论证的前提和结论之间没有一方导致另一方的因果关系，上次考试不影响这次考试，苹果不影响橙子，反之亦然，它们是只在相似对象之间进行类推。

下面详细分析一下削弱题的解法。

方法论

必须区分论证类型。

1 结果型Argument削弱策略：

寻找某种可能性导致预测结果失败。比如：万炜很努力，所以他一定会考好。削弱：他每天都在努力学习错误的方法。这个选项很好，因为它符合前提（万炜很努力），且会使得他不能考好，即让结论成立的可能性降低。

2 解释型Argument削弱策略：

（1）寻找新的原因导致原先有待解释的现象，即给出其他解释；（2）在原文给出的解释不成立的情况下，原文有待解释的现象仍然能够出现，即无因有果。比如：万炜考得特别好，说明他肯定努力了。削弱：他作弊了；他之前不努力的时候考得也很好。这两个选项都很好，前一个给出了万炜考得好的新的解释，而后一个指出在原因没发生的情况下结果也能发生。

3 类比型Argument削弱策略：

寻找某种可能性破坏类比对象之间的相似性，使得类比失败。比如：万炜很笨，所以他的双胞胎妹妹高宇琪肯定也很笨。削弱：万炜小时候脑袋磕过，但高宇琪没有。这个选项好，它破坏了类比对象之间核心特点的相似性。

如果觉得难以判断文章的论证类型，那么请找到一个选项，使得文章前提为真、结论为假，即让文章前提对结论的支持链断裂。请注意，正确选项永远不能违背原文前提。

[例1]

A drug that is highly effective in treating many types of infection can，at present，be obtained only from the bark of the ibora，a tree that is quite rare in the wild. lt takes the bark of 5, 000 trees to make one kilogram of the drug. lt follows，therefore，that continued production of the drug must inevitably lead to the ibora's extinction.

Which of the following，if true，most seriously weakens the argument above?

（A）The drug made from ibora bark is dispensed to doctors from a central authority.

（B）The drug made from ibora bark is expensive to produce.

（C）The leaves of the ibora are used in a number of medical products.

（D）The ibora can be propagated from cuttings and grown under cultivation.

（E）The ibora generally grows in largely inaccessible places.

解析：本文属于结果型论证，基于ibora持续被砍，预测ibora会灭绝。正确选项需要有某种原因可以让ibora被持续地砍，还能不灭绝。所以选D，因为砍下来的ibora还可以继续培养生长，所以砍了也不会灭绝。

正确选项：D。

[例2]

Journalist: ln physics journals，the number of articles reporting the results of experiments involving particle accelerators was lower last year than it had been in previous years. Several of the particle accelerators at major research institutions were out of service the year before last for repairs，so it is likely that the low number of articles was due to the decline in availability of particle accelerators.

Which of the following，if true，most seriously undermines the journalist's argument?

（A）Every article based on experiments with particle accelerators that was submitted for publication last year actually was published.

（B）The average time scientists must wait for access to a particle accelerator has declined over the last several years.

（C）The number of physics journals was the same last year as in previous years.

（D）Particle accelerators can be used for more than one group of experiments in any given year.

（E）Recent changes in the editorial policies of several physics journals have decreased the likelihood that articles concerning particle-accelerator research will be accepted for publication.

解析：本文属于解释型论证，要解释为什么涉及particle accelerator的论文少了，解释是能够做实验的particle accelerator少了。正确答案最可能采取给出其他解释或无因有果。E完美，因为E提供了其他因素，杂志的政策改变不利于涉及particle accelerator的论文发表，可以导致该话题论文发表减少。

正确选项：E。

[例3]

Although the discount stores in Goreville's central shopping district are expected to close within five years as a result of competition from a SpendLess discount department store that just opened，those locations will not stay vacant for long. ln the five years since the opening of Colson's，a non-discount department store，a new store has opened at the location of every store in the shopping district that closed because it could not compete with Colson's.

Which of the following，if true，most seriously weakens the argument?

（A）Many customers of Colson's are expected to do less shopping there than they did before the SpendLess store opened.

（B）lncreasingly，the stores that have opened in the central shopping district since Colson's opened have been discount stores.

（C）At present，the central shopping district has as many stores operating in it as it ever had.

（D）Over the course of the next five years，it is expected that Goreville's population will grow at a faster rate than it has for the past several decades.

（E）Many stores in the central shopping district sell types of merchandise that are not available at either SpendLess or Colson's.

解析：本文是类比型论证，具体来说，和non-discount store Colson's竞争不过，很多店倒闭了，没有关系，倒闭的地方都开了新店。所以，如今竞争不过discount store SpendLess导致很多店倒闭，也肯定会有很多新店开出来。削弱策略应该是破坏类比对象间的相似性。正确选项B准确地指出了此差异，即non-discount与discount的区别。之前虽然因为竞争不过non-discount store Colson's关闭了很多店，但仍然能开出新的店，这些店都是discount store，不和Colson's竞争，重要的是当时没有discount store巨无霸SpendLess。但现在SpendLess出现，使各种discount store倒闭，那么还能开出什么店呢？既竞争不过Colson's也竞争不过SpendLess。

正确选项：B。

[例4]

Astronomers occasionally detect gamma-ray bursts in the sky. Matter crashing onto neutron stars in our galaxy would emit gamma-ray bursts with durations and intensities like those of the bursts observed by astronomers. Therefore，such interactions between matter and neutron stars are，plausibly，the explanation for these bursts.

Which of the following，if true，most strongly undermines the proposed explanation for gamma-ray bursts?

A．Astronomers first detected gamma-ray bursts in 1973，whereas neutron stars were known to exist several decades before that.

B．Astronomers believe that neutron stars are the remnants of stars that once violently exploded and ejected most of their constituent matter.

C．Gamma-ray bursts vary in duration from as little as a thousandth of a second to more than 100 seconds.

D．Gamma-ray bursts occur just as often in regions of the sky where neutron stars are thought not to exist as they do where neutron stars are known to exist.

E．Some neutron stars emit short pulses of radio waves，which are known to be of lower frequency than gamma rays.

解析：本文是解释型论证，为什么天空会有gamma-ray bursts，解释是物质与neutron stars碰撞。削弱策略最有可能是指出其他成因或者无因有果。D答案采取了无因有果的策略，即天空中没有neutron stars的地方照样可以产生gamma-ray bursts。

正确选项：D。

五、假设题（Assumption）

方法论

假设题的难点在于定义中的“依赖”，意味着我们要选择论证成立所需要的“必要条件”，而非“充分条件”。举个例子：“十八岁以上的观众允许入内，所以万炜可以入内。”从字面意思上来说，这个论证显然是不成立的，因为条件不充分。要使论证成立，我们直觉上会补充的条件是：万炜至少十八岁。这个条件就是该论证成立所需要的充要条件，它既充分，也必要。但是，理论上，万炜如果至少十八岁，那么他必须首先至少十七岁、十五岁、三岁……那么“万炜至少十七岁、十五岁、三岁”等也自然成为该论证成立的必要条件，但是显然，这些条件是不足以保证万炜可以入内的，因此它们并不是充分条件。我们会发现，该论证所必须依赖的额外条件理论上有无数个，包括“万炜至少十八岁”“万炜至少十七岁”“万炜至少十五岁”“万炜至少三岁”，等等。

同学们应该此刻能够意识到，“万炜至少十八岁”这个假设和其他假设不同，它是唯一一条既充分、又必要的条件，而其他假设都是必要条件而已。因为这种区分的存在，使得理论上寻找论证假设有两种常见的途径。

充要假设的寻找途径叫“架桥法”，即寻找命题需联系前提与结论中的不同概念。比如，在“哈士奇是狗，所以哈士奇很萌”这个论证中，充要假设就是“狗很萌”；在“GRE考英语，所以GRE很难”这个论证中，充要假设就是“考英语的考试很难”。

必要非充分假设的寻找途径叫“取非削弱法”，即作者的论证要是严谨的，必须假设对他的论证起到削弱作用的情况不出现。所以，如果题目考察的是一个论证所依赖的必要条件，其正确选项的策略就将是排除削弱的情况。我们做题的时候，可以将选项取非，然后看是否能够削弱原文论证，如果能，则该选项就是题目的答案。换言之，因为必要条件是论证成立所必需的，即如果它不成立就会削弱论证。

在目前GRE考试中，当题干中的关键词是“文章依赖以下哪个假设”时，它考查的就是论证的必要条件。这时我们就应该按照以上策略执行，去考察哪个选项排除了削弱的可能性，这个选项就是我们要的答案。比如，在“万炜这次考得很好，说明他先前努力过”这个论证中，作者必须假设“万炜没有作弊”，因为如果万炜作弊了，通过给出其他解释就对原文的论证进行了削弱。

[例1]

Although computers can enhance people's ability to communicate，computer games are a cause of underdeveloped communication skills in children. After-school hours spent playing computer games are hours not spent talking with people. Therefore，children who spend all their spare time playing these games have less experience in interpersonal communication than other children have.

The argument depends on which of the following assumptions?

（A）Passive activities such as watching television and listening to music do not hinder the development of communication skills in children.

（B）Most children have other opportunities，in addition to after-school hours，in which they can choose whether to play computer games or to interact with other people.

（C）Children who do not spend all of their after-school hours playing computer games spend at least some of that time talking with other people.

（D）Formal instruction contributes little or nothing to children's acquisition of communication skills.

（E）The mental skills developed through playing computer games do not contribute significantly to children's intellectual development.

解析：本文是结果型Argument，基于打游戏缺乏交流，预测打游戏的孩子交流能力比其他人差。如果是削弱题，削弱选项就会寻找导致这些打游戏的孩子不比其他人交流能力差的原因。正确答案C取非后的意思是，不打游戏的孩子也不会花时间交流，无论打不打游戏的孩子交流一样差，实现我们想要的效果。

正确选项：C。

[例2]

Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children. Elementary school nurses in Renston report that the proportion of schoolchildren sent to them for treatment of allergic reactions to those chemicals has increased significantly over the past ten years. Therefore，either Renston's schoolchildren have been exposed to greater quantities of the chemicals，or they are more sensitive to them than schoolchildren were ten years ago.

Which of the following is an assumption on which the argument depends?

（A）The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

（B）Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

（C）Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

（D）The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

（E）Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

解析：本文是解释型Argument，为什么去校医院看某两种过敏的孩子多了，给的解释是孩子更多暴露在该过敏源下，或是孩子更敏感了。如果是削弱题，削弱选项最有可能给出其他解释或无因有果。正确答案是C，取非后的意思是，孩子比以前在过敏后更有可能被送去校医院了，可以很好地解释为什么送去看这两种过敏的人多了。

正确选项：C。

六、加强题（Strengthen）

方法论

加强题是最灵活的一种题型。首先，我们需要注意，“加强”不等于“证明”，我们要选的选项是有利于原文论证成立的条件，但不见得要保证原文论证成立，这就导致了加强题的灵活度。一种选项可能直接就明显保证了结论的成立；但还有一种选项可能只是有助于排除削弱的可能性，类似于假设题。我们在做题的时候需要保持这种灵活度。

比如：万炜考试成绩提高了，说明他这次考试之前努力了。直接加强这个论证的选项可能直接说“考试之前每天晚上他都复习到很晚”，这种选项就很明显。但更多情况下，我们遇到的正确答案会类似“这次考试比上次考试更难”。这很不直接地加强了论证，方式是排除了“因为题目简单导致万炜成绩提高”的解释，因此这种选项和假设题的答案很相似，而这是实际考试中我们最常见到的选项，大家必须有所防范，有所预期。

[例]

ln a certain wildlife park，park rangers can track the movements of many rhinoceroses since those animals wear radio collars. When，as usually happens，a collar slips off，it is put back on. Putting a collar on a rhinoceros includes immobilizing the animal by shooting it with a tranquilizer dart. Female rhinoceroses that have been often recollared have considerably lower fertility rates than uncollared females. Possibly，therefore，some substance in the tranquilizer inhibits fertility.

Which of the following，if true，most strongly supports the argument?

（A）The dose of tranquilizer delivered by a tranquilizer dart is large enough to give the rangers putting collars on rhinoceroses a generous margin of safety.

（B）The fertility rate of un-collared female rhinoceroses in the park has been increasing in the past few decades.

（C）Any stress that female rhinoceroses may suffer as a result of being immobilized and handled has little or no negative effect on their fertility.

（D）The male rhinoceroses in the wildlife park do not lose their collars as often as the park's female rhinoceroses do.

（E）The tranquilizer used in immobilizing rhinoceroses is the same as the tranquilizer used in working with other large mammals.

解析：本文是解释型论证，为什么犀牛的不孕率高了，原文的解释是：射向犀牛的镇静剂是罪魁祸首。如果是削弱题，削弱选项很可能会采取给出其他解释或无因有果。正确选项C的意思是，包含镇静剂的标枪射向犀牛后，犀牛被控制、被处理所造成的压力本身不会使得犀牛不孕，排除了犀牛不孕的另一种解释。

正确选项：C。

七、填空题（Logical Completion）

方法论

这种题型会在文章后面留一个空，由考生选择合适的选项填进去使得上下文逻辑合理。其实填空并不是新的题型，所填的空可能是归纳题的结论、解释题的解释、削弱题的反例、加强题的证据。简单来说，它可能是这四种题型的任意一种，因此在这里只需要讲解如何判断拿到的填空题到底是以上哪一种题型。

例1：万炜很努力，而努力的人都能考好，所以_______。

这是归纳题，只需要按照原文逻辑推断出合适结论就可以。判断标准是：空格之前的信息是并列关系，既不是要寻找怪事的解释，也不是要给理由加强一个Argument，空格前的逻辑标志词还提示要填入结论性质的成分。

例2：万炜很努力，但是他总考不好，因为_______。

这是解释题，只需要按解释题的思路做就可以。判断标准是：空格之前的信息是怪事，而空格之前的逻辑词提示要寻找原因。

例3：万炜很努力，所以他一定能考好，因为_______。

这是加强题，只需要按加强题的思路做就可以。判断标准是：空格之前的信息是Argument，而空格之前的逻辑词提示要寻找理由支持这个Argument结论。

例4：万炜很努力，但是这不能证明它一定会考好，因为_______。

这是削弱题，只需要按削弱题的思路做就可以。判断标准是，空格之前的信息说不能推断出某个结论，而空格之前的逻辑词提示要寻找理由，也就是要为削弱某个结论寻找理由。

[例]

Ferber's syndrome，a viral disease that frequently affects cattle，is transmitted to these animals through infected feed. Even though chickens commercially raised for meat are often fed the type of feed identified as the source of infection in cattle，Ferber's syndrome is only rarely observed in chickens. This fact，however，does not indicate that most chickens are immune to the virus that causes Ferber's syndrome，since_______.

Which of the following most logically completes the passage?

（A）chickens and cattle are not the only kinds of farm animal that are typically fed the type of feed liable to be contaminated with the virus that causes Ferber's syndrome

（B）Ferber's syndrome has been found in animals that have not been fed the type of feed liable to be contaminated with the virus that can cause the disease

（C）resistance to some infectious organisms such as the virus that causes Ferber's syndrome can be acquired by exposure to a closely related infectious organism

（D）chickens and cattle take more than a year to show symptoms of Ferber's syndrome，and chickens commercially raised for meat，unlike cattle，are generally brought to market during the first year of life

（E）the type of feed liable to be infected with the virus that causes Ferber's syndrome generally constitutes a larger proportion of the diet of commercially raised chickens than of commercially raised cattle

解析：这是削弱题，并且文章类型是解释型Argument，文章试图解释为什么鸡并不会出现该病的症状，暗示要去削弱的解释是鸡对该病毒免疫。正确选项D指出，鸡还没来得及出现症状就已经被卖掉了，所以提供了新的合理解释。

正确选项：D。