关于OG90，我觉得题目出得有问题

90.

The sustained massive use of pesticides in farming has two effects that are especially pernicious. First, it often kills off the pests' natural enemies in the area. Second, it often unintentionally gives rise to insecticide-resistant pests, since those insects that survive a particular insecticide will be the ones most resistant to it, and they are the ones left to breed.

From the passage above, it can be properly inferred that the effectiveness

of the sustained massive use of pesticides can be extended by doing which of the following, assuming that each is a realistic possibility?

(A)Using only chemically stable insecticides

(B)Periodically switching the type of insecticide used

(C)Gradually increasing the quantities of pesticides used

(D)Leaving a few fields fallow every year

(E)Breeding higher-yielding varieties of crop plants

我觉得90题不够严谨。

它谈到两个问题，关于杀虫剂的害处。

1是杀死了害虫的天敌

2是增加了抗药性

然后问哪一种方法能更有效的解决以上问题，或更有效果。

这题所有的五个答案都是针对第2种情况，即如何消除抗药性设置的。实际上对于答案B，虽然能有效的解决第2类问题，但是使第1类问题的效果更差。（我的逻辑假设是这样的：不停的换杀虫剂将使害虫的天敌死得更惨，所以，这一题无正解，五个答案逻辑都有问题）

所以，至少在这一题上，OG的出题人不够严谨，思路不清晰。。。

不过答案D虽然不会使第二类效果变好，但使第一类效果有些缓解。所以，呵呵。。。真有趣，这个题目，NND

GMAT是很忌讳用自己的常识去推断文章。GG想太多了。

似我等生物白痴看了文章就理解为：持续使用杀虫剂才会杀死益虫和害虫产生耐药性。并没有理解为一使用杀虫剂就把益虫全杀死了。否则这杀虫剂一定是伪劣产品，害虫要持续用才杀死，益虫倒一用就杀死了。

肤浅的理解：仅供一笑。

请注意题目的scope是什么. effectiveness of the sustained massive use of pesticides - 大量使用 pesticides 的有效性.

少量使用pesticides, 不使用pesticides, 或其他方法(生物杀虫)等 are not within the scope of this question.