求助OG12—74题！

soojin3215

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

这题答案是D，我错选成E.解释中说一个发生在1972年的agreement用的时态应该是past tense，所以应该用reduced。
可是我觉得这个agreement的效果是减少了倾倒量，这是一个事实，应该用一般现在时，用reduces也是对的。请问为什么这里要用reduced呢？？

谢谢各位！！

soojin3215

我有一点不太明白
这个agreement所签署的初始目的是为了allow to dump还是为了reduce排放量呢？
如果目的是允许dump那为什么达到的效果是reduce the amount了呢？
这个是逻辑上的矛盾么

soojin3215

这个agreement所签署的初始目的是为了allow to dump还是为了reduce排放量呢？