[求助]lsat逻辑，请教

忘记了 · 发表于 2009-3-8 17:19:00

Most parents who are generous are good parents, but some self-centered parents are also good parents. Yet all good parents share one characteristic: they are good listeners.

If all of the statements in the passage are true, which one of the following must also be true?

A. All parents who are good listeners are good parents.

B. Some parents who are good listeners are not good parents.

C. Most parents who are good listeners are generous.

D. Some parents who are good listeners are self-centered.

E. Fewer self-contered parents than generous parents are good listeners.

The correct choice should be D~, but I voted for B. Actully, I could not tell the difference between B and D.

Open to discuss.

crusoecrusoe · 发表于 2009-3-8 17:34:00

开始我也选择B，不过看到D，发现D不仅是最好而且是must be true.

你画一个图，就应该发现，题干只是说good parents成立，必然 good listeners，而前者不成立，后者未必成立，是典型的充分条件关系，因此，B自然是错误的认为二者是充要条件了。

D是文中很明确可以看出来的，画图后会很明确。

忘记了 · 发表于 2009-3-8 17:47:00

其实是不是这样理解，B选项可能是对的，但不一定是对的，但是D选项一定是对的？然而题目问的是must be true。the parents who are good listeners有三种可能，选项用some表达了其中一种，但是选项B因为否定，是限制了其他可能，是不是可以这样理解？

其实做题目的时候我有画图，就是不明白这两句的区别，绕进去绕不出来了

[此贴子已经被作者于2009-3-8 17:50:47编辑过]

crusoecrusoe · 发表于 2009-3-8 20:49:00

B选项，从题目中所给的信息，不能证明其对，也同样不能证明其错，但其有错的可能性，因此不能是must be true。

其实啊，做题就是做题，只选最true的，绝不选可能true的，对于B选项的不周延，不要考虑太多。

[求助]lsat逻辑，请教

[求助]lsat逻辑，请教

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