何时需要在平行结构前加介词？

zzwho

先贴到题目吧，OG13里的：

Most efforts tocombat such mosquito-borne diseases like malaria and dengue have focused either onthe vaccination of humans or on exterminating mosquitoes with pesticides.

(A) like malaria and dengue have focused either on thevaccination of humans or on exterminating

(B) like malaria and dengue have focused either onvaccinating of humans or on the extermination of

(C) as malaria and dengue have focused on eithervaccinating humans or on exterminating

(D) as malaria and dengue have focused on eithervaccinating of humans or on extermination of

(E) as malaria and dengue have focused on eithervaccinating humans or exterminating

我的问题：SC已经做了和总结了不少，感觉也初有成效，但今天遇到这道题时忽然迷惑了，因为我印象中做过平行结构前需要补充介词的情况，所以希望大侠们能帮我clarify一下：平行或比较结构的情况下，何时我们需要补充介词，何时只要补充宾语呢？是不是如果在一个动词之后，并且介词一样的情况下，我们就不需要再补出介词了呢？像这题这样？求解答啊.....

PS：这题的答案是E


谢谢你们啦~~！！

zzwho

另外，我前面这个帖子也已经沉很久了，如果你看到了，也帮我回答下吧，一个很小很小的问题，谢谢了~~ http://forum.chasedream.com/thread-872548-1-1.html

zzwho

求回复啊...求回复...

览物之情

不知道现在回复你还有用不。我自己的理解是平行的是either or中间的部分和or后面的部分。所以如果是focus on either A or B. B 前面就不加ON。如果是focus either on A or on B .就加ON.   Ron 的视频讲过I like to run and swim.和i like to run and swim 都是对的。因为只是要and前后平行。但是i like both to run and to swim就一定要加to.因为是both and 中间的部分和后面的平行。