Sentence Correction

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


OA: D

This question has been discussed many times but, still, understanding it is pain for many students, including me. Most students choose "A" thinking that "1972 agreement reduced the amount that municipalities were allowed to dump before 1972". E.g. before 1972, municipalities were allowed to dump 10 tonnes per day but after 1972 municipalities were allowed to dump 8 tonnes per day. I think one way to understand it forever would be ask "how would one write the sentence that actually describes the meaning in BOLD and then see the difference between that sentence and correct answer.

Experts can you please help in writing the sentence that actually describes the meaning in BOLD