GMAT训练 | CR解析：Must Be True 演绎类题型
作者 / Linhui Fu, 编辑 / NativeS.
本文为“GMAT公益训练”的第2篇原创知识分享，内容源自Linhui老师5月31日的CR逻辑训练。
在NativeStudy，我们长期坚持每天2小时的公益指导，邀您一起，学习坚持：GMAT训练计划。
Critical Reasoning （批判性推理）作为以逻辑能力为代表的典型题目，更是需要你时时刻刻保持清晰的思路。就CR而言，CR Bible逻辑圣经给我们提供了一套很实用的思考体系。今天我们将带大家了解CR当中的一个重点题型：Must be true 演绎题
Evaluate评价题的常见提问方式：
If the statements above are true, which of the following must be true?
Which of the following conclusion is best supported by the statements above?
The statements, if true, best support which of the following assertions?
Which of the following can be correctly inferred from the statements above?
Which of the following is most strongly supported by the information above?
Must be true要求我们根据stimulus中的已知条件去推测一个*必然成立*的结论。解题的时候，如果要用一句话来概括Must be true题目的解题要点的话，我们会说：选项的一切以stimulus为纲。
也就说你选的这个选项必须是从原文能够推理出来的，必须在原文中有根据。通常，这个正确答案是对原文某一句话的同义重复或改述，或者是原文某两或三句话能推出来的*必然成立*的结论。在Must be true当中，你去判断每个答案的时候都一定要去原文找根据，问问自己：原文中有提到过这个选项的内容吗？ 或者问问自己：根据原文的信息，选项里的信息一定成立吗？ 如果答案是no的话，那么这个选项就不是正确答案。
常见的错误答案形式包括：你的选项带有原文没有提到过的新信息，或者你的选项与原文矛盾。
以下例题摘自Verbal 2nd分册
A computer equipped with signature-recognition software, which restricts access to a computer to those people whose signatures are on file, identifies a person’s signature by analyzing not only the form of the signature but also such characteristics as pen pressure and signing speed. Even the most adept forgers cannot duplicate all of the characteristics the program analyzes.
Which of the following can be logically concluded from the passage above?
(A) The time it takes to record and analyze a signature makes the software impractical for everyday use.
(B) Computers equipped with the software will soon be installed In most banks.
(C) Nobody can gain access to a computer equipped with the software solely by virtue of skill at forging signatures.
(D) Signature-recognition software has taken many years to develop and perfect.
(E) In many cases even authorized users are denied legitimate access to computers equipped with the software.
原题解构-逻辑释义
Premise 1: 一个新的签字识别软件会允许电脑只开放给签字有记录的人，这个软件确定人选的时候会同时依靠字体形式和其他特点，比如签字笔压和速度。
Premise 2: 即使是技艺最精湛的伪装者也不可能同时复制软件会分析的这些特点
(A) The time it takes to record and analyze a signature makes the software impractical for everyday use.
(A) “软件记录和分析指纹需要消耗的时间导致软件不可能用于日常工作” 。
逐项分析：新信息，原文未提到软件需要花多久时间，也未提到软件是否适合每日工作还是只适合高端工作。
(B) Computers equipped with the software will soon be installed In most banks.
(B) “装有这种软件的电脑会很快在大多数银行内安装”。
逐项分析：新信息，虽然B选项提到的事情是很可能发生的，但是也不一定会发生，也有可能这套软件太贵而银行不愿意安装，也有可能软件还未大规模投产，银行不能马上安装。这些可能性都存在，所以B选项不是一个*必然成立*的结论。
(C) Nobody can gain access to a computer equipped with the software solely by virtue of skill at forging signatures.
(C) “没人能仅仅通过高超的伪装技艺来接近装有这种软件的电脑”。
逐项分析：正确。
我们需要联系两个Premise来理解：一方面软件要求同时满足N个标准才放行（字体形式，笔压，速度等），另一方面，没有人能同时伪装所有的技能。所以没人能同时满足软件的所有审核标准，自然也没有人能够通过伪装骗过软件，接触到装有这个软件的电脑了。
(D) Signature-recognition software has taken many years to develop and perfect.
(D) “人们花了很多年去发明和完善签字识别软件”。
逐项分析：新信息，原文未提到研发这种软件的时间有多长，可能是花了很长时间，也可能是很快就研发出来了。排除。
(E) In many cases even authorized users are denied legitimate access to computers equipped with the software.
(E) “很多时候即使是被授权的用户也可能被软件拒绝使用此种电脑”。
逐项分析：这属于新信息，原文只说了伪装者不可能入侵这种电脑，却没有提到过软件是否会错误地拒绝授权者。注意伪装者和授权者是两批不同的人，不要把他们混在一起。如果软件拒绝了伪装者，那么这是说明软件工作正常。 如果软件拒绝了授权者，那说明软件犯错了，因为软件本身就是要设计来让这些授权者是可以使用的。原文并未告诉我们软件是否会犯这种错误。
Laws requiring the use of headlights during daylight hours can prevent automobile collisions. However, since daylight visibility is worse in countries farther from the equator, any such laws would obviously be more effective in preventing collisions in those countries. In fact, the only countries that actually have such laws are farther from the equator than is the continental United States.
Which of the following conclusions could be most properly drawn from the information given above?
(A) Drivers in the continental United States who used their headlights during the day would be just as likely to become involved in a collision as would drivers who did not use their headlights.
(B) In many countries that are farther from the equator than is the continental United States, poor daylight visibility is the single most important factor in automobile collisions.
(C) The proportion of automobile collisions that occur in the daytime is greater in the continental United States than in the countries that have Daytime headlight laws.
(D) Fewer automobile collisions probably occur each year in countries that have daytime headlight laws than occur within the continental United States.
(E) Daytime headlight laws would probably do less to prevent automobile collisions in the continental United States than they do in the countries that have the laws.
原题解构-逻辑释义
Premise 1: 要求白天用汽车前灯的规定会减少碰撞
Premise 2: 白天可见度在远离赤道的地方更差，所以这种规定在原理赤道的地方更有效
Premise 3: 唯一一个有这样的规定的地区离赤道的距离比美国大陆离赤道的距离更远
(A) Drivers in the continental United States who used their headlights during the day would be just as likely to become involved in a collision as would drivers who did not use their headlights.
(A) “在美国的司机如果在白天使用前灯的话，他们会和那些不用前灯的司机一样容易卷入车祸”。
逐项分析：原文第一句就提到，如果使用前灯是可以减少碰撞的。这和原文矛盾，排除。
(B) In many countries that are farther from the equator than is the continental United States, poor daylight visibility is the single most important factor in automobile collisions.
(B) “在很多比美国离赤道更远的国家，白天较差的可见度是造成碰撞事故的唯一的最重要的原因”。
逐项分析：原文确实提到了可见度差的地方使用前灯的效果更好，说明可见度差确实非常容易导致事故。可是原文没有告诉我们可见度差是“唯一的，最重要”的原因，这属于在程度上进行夸大。排除。
(C) The proportion of automobile collisions that occur in the daytime is greater in the continental United States than in the countries that have Daytime headlight laws.
(C) “白天的碰撞事故的比例在美国大于真正有这些规定的国家。”
逐项分析：这个选项属于新信息，首先原文并未直接告诉我们各个国家的白天碰撞事故所占的比例，其次，就算我们自己假设白天可见度越差的国家，白天的碰撞事故的比例可能更大，那么在美国这个数据也该更小才对，因为美国的能见度好于真正有这些法律的国家。排除。
(D) Fewer automobile collisions probably occur each year in countries that have daytime headlight laws than occur within the continental United States.
(D) “美国的每年国内的车辆碰撞事故的数量比那些真正有这些法律的国家的碰撞事故数量更多”。
逐项分析：错误原因和C选项相同，引入了新信息，原文只告诉了我们在哪个国家法律更有效，并未告诉我们各国的碰撞事故谁更多谁更少。排除。
(E）Daytime headlight laws would probably do less to prevent automobile collisions in the continental United States than they do in the countries that have the laws.
(E) “ 此法律在美国防止碰撞的效果比不上在真正有这些法律的国家的效果”。
逐项分析：如下图所示，原文提到越远离赤道效果越好，有此规定的国家距离赤道比美国距离赤道远，那么可以推出，在真正有这个规定的国家，此规定的效果好于它在美国的效果。这正是E选项说的意思，E只是换了一个方法，说美国的效果更差。
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作者简介：Linhui FU，NativeStudy高分导师，兼原创撰稿人。美国乔治华盛顿大学硕士，Business Analytics项目。热爱绘画、音乐、健身、潜水、哲学。同时拥有严谨的逻辑能力和巨大的脑洞，是一枚感性与理性互相拉扯的精分患者。其教授的Bible课程体系广受欢迎，GMAT授课课时已累计过千，受益学生超500人。曾四次组织大型公益课程，并撰写了《GMAT OG16CR新题解析》。
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