请教LSAT17-III-19,20，谢谢！

greenfish

19. Train service suffers when a railroad combines commuter and freight service. By dividing its attention between its freight and commuter customers, a railroad serves neither particularly well. Therefore, if a railroad is going to be a successful business, then it must concentrate exclusively on one of these two markets.
For the argument to be logically correct, it must make which one of the following assumptions?
(A) Commuter and freight service have little in common with each other.
(B) The first priority of a railroad is to be a successful business.
(C) Unless a railroad serves its customers well, it will not be a successful business.
(D) If a railroad concentrates on commuter service, it will be a successful business.
(E) Railroad commuters rarely want freight service as well.
为什么是C？我选A，其余四个都觉得可排除。
20. Most people in the United States view neither big nor small business as particularly efficient or dynamic and regard both as providing consumers with fairly priced goods and services. However, most people consistently perceive small business as a force for good in society whereas big business is perceived as socially responsible only in times of prosperity.
The statements above, if true would provide the strongest support for which one of the following hypotheses?
(A) Most people in the United States give little thought to the value of business to society.
(B) If big business were more efficient, it would be perceived more favorably by the public generally.
(C) If small business were regarded as being more dynamic, it too, would receive strongly favorable ratings only in times of general prosperity.
(D) Even if people did not regard big business as providing consumers with value for their money, they would still regard it as socially responsible in times of general prosperity.
(E) Many people in the United States regard the social responsibility of big business as extending beyond providing consumers with fairly priced goods and services.
答案是E。这题就看不大懂了，题目中前后两句有什么关联？

mindfree

1. 正相反, A是无关选项. 你要把握assumption的原则:原文逻辑的必要条件. 原文的逻辑必然有一个gap, assumption用来填补gap. 我讲过assumption的类型, 你可以看看我以前的回复.

此题的逻辑关系中有一个很明显的gap: 概念的跳跃. serve both-->serve neither well==>successful -->serve only one. 这里successful和serve customer well被联系在一起, 但是并没有指出关系. 就是gap. C是标准答案.

A也许可以做为你个推理或结论的答案. 如果你选了A说明你对assumption的题目还没有很了解. 不知道你看的参考书是哪一本?

2. 用排除法. 前四项都是无关选项. E比较绕, 但是符合原文. 大多数人认为BB总是能提供fairly priced goods, 但是认为BB只在经济繁荣时socially responsible.

joywzy

以下是引用mindfree在2003-5-7 21:42:00的发言：
此题的逻辑关系中有一个很明显的gap: 概念的跳跃. serve both-->serve neither well==>successful -->serve only one. 这里successful和serve customer well被联系在一起, 但是并没有指出关系. 就是gap. C是标准答案.

这题我也会选A，对假设也不行啊。 mindfree,能不能推荐什么好的参考书，可以开窍 一下？

概念的跳跃. serve both-->serve neither well==>successful -->serve only one. 这里successful和serve customer well被联系在一起, 但是并没有指出关系. 就是gap. C是标准答案.

那么D呢？也是serve one，也是答案吗？

谢谢。

谢谢。

mindfree

陈向东的书可能有帮助(本人多次推荐此书,世界知识出版社应该为CD的会员打5折). 由于题目中有明显的gap, 这里只有C是标准答案. D是结论题型中的典型错误答案. 原文的逻辑是serve one是成功的必要条件, D说它是充分条件.

joywzy

MINDFREE,

概念的跳跃. serve both-->serve neither well==>successful -->serve only one. 这里successful和serve customer well被联系在一起, 但是并没有指出关系. 就是gap. C是标准答案.

这个就是你上次教我的确认逻辑关系中的假设题。假设一定要是必要条件，不能是充分条件。你举过类似的例子的。

怎么换了个长相，我就认不得了。

greenfish

以下是引用mindfree在2003-5-7 21:42:00的发言：
此题的逻辑关系中有一个很明显的gap: 概念的跳跃. serve both-->serve neither well==>successful -->serve only one. 这里successful和serve customer well被联系在一起, 但是并没有指出关系. 就是gap. C是标准答案.

谢谢mindfree！你说successful -->serve only one，那如果C改成是是serve commuter well呢？是不是还选C？

A也许可以做为你个推理或结论的答案. 如果你选了A说明你对assumption的题目还没有很了解. 不知道你看的参考书是哪一本?

我看的就是CXD的书，不过可能还没吃透。说实在的，我不喜欢看那些文字说明，用例子讲解的会好些。

2. 用排除法. 前四项都是无关选项. E比较绕, 但是符合原文. 大多数人认为BB总是能提供fairly priced goods, 但是认为BB只在经济繁荣时socially responsible.

明白了，谢谢！

mindfree

以下是引用greenfish在2003-5-8 8:34:00的发言：
谢谢mindfree！你说successful -->serve only one，那如果C改成是是serve commuter well呢？是不是还选C？

这个问题很好. 在此题中改变后C就不是答案. 因为可以只serve freiht customers而不serve commuters. 所以必要条件是无论serve哪一个, 都要serve well.

很多假设题目的答案是很多假设其中的一个,别比如说:考砸了-->没复习好. assumption就有很多: 不是考前没睡好造成的;不是考试时晕到了;不是考试时睡着了; 复习好就能考好等等. 答案就是其中一个,比相当于一个集合中的factor.

如果把原文改动一下:
Train service suffers when a railroad combines commuter and freight service. By dividing its attention between its freight and commuter customers, a railroad serves neither particularly well. Therefore, if a railroad is going to be a successful business, then it must expand its resources to serve both well.

那么改动后的C就是正确答案, 因为必须要serve commuter. 此答案也可以是Unless ...serve freight customers well, ...

joywzy

还是不大好理解改动前和改动后的区别?能再讲讲吗?谢谢.

为什么改动后,必须要serve commuter. 此答案也可以是Unless ...serve freight customers well, 这两个都可以是答案呢?

我想也是跟原来的一样,必须是serve customers,两个都必须服务好.

有什么差别吗?不明白.

greenfish

以下是引用mindfree在2003-5-9 2:15:00的发言：

这个问题很好. 在此题中改变后C就不是答案. 因为可以只serve freiht customers而不serve commuters. 所以必要条件是无论serve哪一个, 都要serve well.

明白了！原来我是把C中的customers理解成freight  customers，忽略了也可以是commuter customers，真是惭愧！

greenfish

以下是引用joywzy在2003-5-9 10:27:00的发言：
还是不大好理解改动前和改动后的区别?能再讲讲吗?谢谢.

为什么改动后,必须要serve commuter. 此答案也可以是Unless ...serve freight customers well, 这两个都可以是答案呢?

我想也是跟原来的一样,必须是serve customers,两个都必须服务好.

因为改动前是在现有基础上要成功，就必须服务好其中一个，此时C中的customers可以是freight  customers（充分条件一），也可以是commuter customers（充分条件二）；改动后则是要成功的话，必须加大力度，把两个都服务好（充分条件）。unless服务好commuter （必要条件之一），或服务好freight （必要条件之二），才能成功。
不知这样解释行吗？