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

二位道友，呵呵。

因为我以前学过生物，这个题是生物的逻辑题，就是杀虫剂的解决方案，象这几个方案都有分析过，而且都不可行。最好的方案是用生物方法杀虫（扯远了），因为实际上是这样的，如果换杀虫剂，对天敌确实杀伤性非常大，呵呵。所以，不提倡换杀虫剂。换杀虫剂有灭绝的效果。

我觉得这五个题的答案都不合适，比如看下个题，如果按照90题的逻辑

134.

Caterpillars of all species produce an identical hormone called "juvenile hormone" that maintains feeding behavior. Only when a caterpillar has grown to the right size for pupation to take place does a special enzyme halt the production of juvenile hormone. This enzyme can be synthesized and will, on being ingested by immature caterpillars, kill them by stopping them from feeding.

Which of the following, if true, most strongly supports the view that it would not be advisable to try to eradicate agricultural pests that go through a caterpillar stage by spraying croplands with the enzyme mentioned above?
（此题与90题矛盾，就参考此题目思路了）

(A) Most species of caterpillar are subject to some natural predation.

(B) Many agricultural pests do not go through a caterpillar stage.

(C) Many agriculturally beneficial insects go through a caterpillar stage.

(D) Since caterpillars of different species emerge at different times, several sprayings would be necessary.

(E) Although the enzyme has been synthesized in the laboratory, no large-scale production facilities exist as yet.

实际上这题最大的问题就是，如果这种杀虫剂对beneficial insects造成大规模杀伤的话，就不好用。

而90题忽略了换杀虫剂（当然是sustained的）所带来的杀伤效果。而且这个效果不好检测，就是说，效果一的破坏和效果二的收益倒底是什么样的，有待考证。

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.