77. A 1972 agreement between Canada and the United Statesreduced the amount of phosphates that municipalities had been allowed to dumpinto 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
C为啥是正确答案。OG说关于时态的问题，没看懂。
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