about a of b that结构指代的问题

a of b that 定语从句是到底修饰a还是b？

eg：

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

A中THAT说修饰phosphate 或者修饰amount 都可以，到底是修饰哪个？

BTW，想问下这里E 错再哪里啊，        A 1972 agreement 一份1972年签署的文件未必一定要用过去时啊，它可以从签署之日其就开始作用到至今，并一直这么作用下去，所以用一般现在时有何不对啊，是不是allow一定要用 to but not for？

A中THAT说修饰phosphate 或者修饰amount 都可以，到底是修饰哪个？

修饰的是phosphate。

原因：that从句中没有宾语。that municipalities had been allowed to dump into the Great Lakes.中dump 什么 into the Great Lakes。按照意思应该是倒入湖中的phosphat的总量减少了。

如果修饰的是amount的话，就变成“倒amount入湖中”意思不正确

另外allow sb to do/sb is allowed to do这里是过去完成时

allow for的话不复合习惯用法。

"something is allowed for reason" maybe is right但这里用似乎不对

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

错误地方

1.过去时，

现在时牵强

2.allow for doing不对

小子回复的很快嘛，谢谢，说得有理

这里为啥现在时牵强？我不是说了嘛，1972年制定执行得东西就不能延续至今吗？觉得很奇怪

还有，照这题看来A OF B结构还是就近修饰老？这么理解对伐？