两道逻辑,请教

zephyr1977

18. In experiments in which certain kinds of bacteria were placed in a generous supply of nutrients, the populations of bacteria grew rapidly, and genetic mutations occurred at random in the populations. These experiments show that all genetic mutation is random.

Which one of the following, if true, enables the conclusion to be properly drawn?

(A) Either all genetic mutations are random or none are random.

(B) The bacteria tested in the experiments were of extremely common forms.

(C) If all genetic mutations in bacteria are random, then all genetic mutations in every other life form arc random also.

(D) The kind of environment in which genetic mutation takes place has no effect on the way genetic mutation occurs.

(E) The nutrients used were the same as those that nourish the bacteria in nature.

20. Calories consumed in excess of those with which the body needs to be provided to maintain its weight are normally stored as fat and the body gains weight. Alcoholic beverages are laden with calories. However, those people who regularly drink two or three alcoholic beverages a day and thereby exceed the caloric intake necessary to maintain their weight do not in general gain weight.

Which one of the following, if true, most helps to resolve the apparent discrepancy?

(A) Some people who regularly drink two or three alcoholic beverages a day avoid exceeding the caloric intake necessary to maintain their weight by decreasing caloric intake from other sources.

(B) Excess calories consumed by people who regularly drink two or three alcoholic beverages a day tend to be dissipated as heat.

(C) Some people who do not drink alcoholic beverages but who eat high-calorie foods do not gain weight.

(D) Many people who regularly drink more than three alcoholic beverages a day do not gain weight.

(E) Some people who take in fewer calories than are normally necessary to maintain their weight do not lose weight.

18为什么选A? 20为什么不选A? 请赐教.[em09][em09][em09]

zyh79

2。a答案只是从其他途径避免超过。实际上，就算其它一点不摄入，他也早已超过了  
intake necessary 。
1。这道题，我思考了很久。
  A确实很难否定掉，但和D比，A的假设太强，它可以作为很多种情况的的假设，而无需大谈环境不环境的，不太适合本题。
对了，这是不是lsat，若是，下次麻烦放到lsat专刊，谢谢

Kilroy

18为什么不选选C？ 通过细菌的遗传变异是随机的，推出所有动物的变异是随机的。
20 选B？

提问题最好留下个标准答案，以便大家核对自己的判断

zephyr1977

对不住，答案是18A,20B,
下回放到专刊一定。

tongxun

18、若将结论修改成：These experiments show that all this certain kinds of bacteria  genetic mutation is random. 选项D就成立了。
20、A选项，不管这个人是否又吃了肥猪肉，他现在的脂肪摄入量已经是超标了。还应该增肥。因此，这个选项没有解决矛盾。

z_weining

18题：
先用“有关无关”和“求同求异”的方法判断，
a,或者所有都是随机，或者没有是随机的。原文中，提到了“所有”，也提到了“随机”，所有信息有关。放下。
b,试验中的细菌是一般形式。只说了“细菌”有关，所以试无关选想。
c,如果细菌中的所有变异都是随机的，那么其他生命的变异也是随机的。只提到了“随机”试有关的，“其他生命的变异”原文中没提。所以无关。
d,发生变异的环境对基因变异没有影响。有关，放下。
e,营养和细菌的营养一样，显然无关。
可恶的是，a和d都表示求同，但a 明显要比d好，因为：
a说的是“或者所有都是随机，或者没有是随机的。”，但是原文已经告诉我们，“genetic mutations occurred at random in the populations”，所以，就排除了a的后半句话了，那么就只剩下前半句的原文结论了。

但是这个提还是有点变态，怎么能出现两个求同答案呢！！ft，我想gmat中应该不会那么变态吧，虽然我还没做过lsat题。

z_weining

关于20题，我和楼上的一些大虾的意见可能不一样。
我觉得，关键在于一个词“some”。这个词都只能表示“子集”的概念。但我们要解释“全集”的矛盾。
如果a把some去掉，那么也应该是正确答案！！
但如果那样，题就出错了！！嗬嗬！

tongxun

我有不同看法：题干中已经说明了2-3杯已经过量。

z_weining

但是没说过两后会有什么结果。
文中没有的，我们不能推！！我们都是“傻子”：））

tongxun

请看：drink two or three alcoholic beverages a day and thereby exceed the caloric intake necessary to maintain their weight ------------consumed in excess of those with which the body needs to be provided to maintain its weight are normally stored as fat and the body gains weight.