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
求问这个题目为什么A的过去完成时不正确呀？我感觉可以理解为过去减少了（之前：过去的过去的允许的数额），求指导 谢谢大家!
