SC99

qiufeng1990

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.)

b) reduced the amount of phosphates that municipalities were allowed to dump
c) reducs the amount of phosphates that municipalities have been allowed to dump

???????那位请分析一下时态？？？

tongxun

既然是1972年的事情，C中的现在式不妥。
我认为应该用A 的表达，前面是一个过去发生的事情，后者为在此之前发生的事情。