OG 13的 SC77，正确答案的句子结构不理解，求解释

melodyflying

77.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

答案是D，这样正确的句子就是：A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities are allowed to dump  into the Great Lakes.
“that municipalities are allowed to dump into the Great Lakes”是做什么成分？
定语从句？

pye348789

现在完成时就变成了
两国同意减少 市民已经倾倒P的量  （意思是你得去水里把P 捞出来）

原意是
两国同意减少 市民倾倒P的量

Steven0124

我还想问下 既然是对现在的影响为什么不用现在完成时呢??? 就是allow那里... have been allowed to dump 有什么不对么?
既然are allowed 为什么不能说是过去发生的事(agreement)对现在人的影响呢???

寻找NN ing...

xiaoguolulu

phosphates的同位语。