求助一道OG语法~~~

陌下清风

A 1972 agreement between Canada and U.S. reduced the amount of phosphates that municipalities had been allowed
  to dump into the Great Lake.
   (A) reduced the amount of phosphates that municipalities had been allowed to dump
   (B) reduced the phosphates amount that municipalities had been dumping
   (C) reduced the phosphates amount municipalities have been allowed to dump
   (D) reduced the amount of phosphates that municipalities are allowed to dump
   (E) reduced the amount of phosphates allowed for dumping by municipalities

这道题答案为D，那A呢？是因为时态问题吗？希望大家可以帮我解答一下~~谢谢喽~`

陌下清风

自己顶一下~

liushmh

我觉得这个是逻辑关系决定的
如果用过去完成时，则表示过去一直都在倒，而从1972年到现在已经不能再往湖里面倒phosphates。
但是句子用的是reduce，表示减少倾倒量，而并没有禁止，减少量就意味着一直都在往湖里面倒phosphates，所以用现在时态比较符合。