OG-134请教

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?

(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.
                    C

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

题是做对了，不过“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. ”不知道怎么翻译，请教nn

我正在做这题呢。认为答案是C~。杀害虫的时候，把益虫也杀了，不是不明智的举动吗？

对了，这题好多生词，看不明白，是查过后才得出C……

自己的问题忘了写了：题干中 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.  做题略读的时候这句的大概意思能懂，但是回头细读的时候被这句的结构给弄糊涂了。

请教nn这句正常顺序是不是这样：A special enzyme halt the production of juvenile hormone to take place only when a caterpillar has grown to the right size for pupation？

我认为理解advisable是关键，advisable的解释是，something advisable should be done in order to avoid problems or risks.这里的就是指eradicate agriculturally beneficial insects吧