想问下OG62和大全2

    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（A）

(E) reduces the amount of phosphates allowed for dumping by municipalities

这里答案是A,OG上是D,到底是哪个哈~~

我选A的时候它是D,我选D的时候它是A,我疯了

A

dumping happened before agreement. the verb forms employed in A clearly show the chronological sequence.