请教各位前辈一个问题OG13-SC 77

yingying_0729

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

这里的正确答案是D。
但是我是在C和D里面有些徘徊。对于C：我觉得1972是一个定语，修饰agreement，所以这其实是一个名词，可以用reduces的时态，而且have been allowed可以表示从1972到现在都是起作用的。但是这句话有个缺陷就是phosphate amount表达的很别扭。
对于D，不太明白为什么要用过去式和are allowed。
请各位前辈指点，谢谢。

brfmzbjz

1972 agreement 是一个名词
但是很明确描述了这个事情发生在过去
没有理由用reduces

关于 have been allowed 和 had been allowed

要注意  the municipalities had/have been allowed to dump 是放在一个从句里修饰 1972 agreement reduced 的amount
也就是说 A 要 reduced的是历史里已经发生的东西 这个不符合逻辑 是因为
你没办法回到过去(也就是1972 areement之前），去改变历史里 the municipalities 被允许丢弃的量。
D 被允许的丢弃量 要么是现在也有效的 (要用 are allowed) 要么是过去那些年有效现在已经失效( 用were allowed) 它强调的是一个当下的状态 而不是一个start in the past and continue into the present的动作
比方说 你可以说
the food you are allowed to eat =现在仍然允许吃
the food you were allowed to eat =过去某个时候允许 现在已经不允许
但很难说成 the food you have been allowed to eat 因为这里不是要强调be allowed 这个动作跨越至今

个人理解