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.
看了好多帖子,大都围绕A选项讨论,我。。。我。。选的是C选项。。还是不明白为什么have been allowed 不对呢??求牛牛解答。。 Og 12-74. 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
不好意思......我还是有疑惑 og 解释说用are allowed, if the agreement remained in effect when sentence was written......我觉得这样子的话为什么不能用have been allowed 呢?have been allowed 不也是remained in effect when sentence was written????