OG12-74 时态问题

crystal509

A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes.
(A)    reduced the amount of phosphates that municipalities had been allowed to dump
(B)    reduced the phosphate amount that municipalities had been dumping
(C)    reduces the phosphate amount municipalities have been allowed to dump
(D)    reduced the amount of phosphates that municipalities are allowed to dump
(E)    reduces the amount of phosphates allowed for dumping by municipalities
答案为D
我想问为什么这里不能用现在完成时呢？

lordwilliam

首先that从句是修饰amount of phosphate的（就近法则），不是主名词agreement，所以从句时态要符合amount of phosphate的表述意思，且不需要和主语的时态一定一致。 e.g. I believe this is his book, which was bought last year.

这里表述的意思是说"自治州的人(had been allowed -- “以前被同意”但是当这条agreement发布的时候“已经不再存在”)/(are allowed -- “被同意”并且当这条agreement发布的时候“依然存在”）/（was allowed -- “以前被同意”但是当这条agreement发布的时候“不再存在”）to dump into the Great Lake。注意前面用了reduce这个词，说明这个agreement正在减少一个还依然存在的现象，所以这里只有are allowed合适。

有人会问那have been allowed对吗？其实have been/had been allowed都是表示“已经发生并且现在已经结束的意思”唯一的不同在于have说明以前发生，had说明以前的以前发生。