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题库 / OG13-SC-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.
reduced the amount of phosphates that municipalities had been allowed to dump
reduced the phosphate amount that municipalities had been dumping
reduces the phosphate amount municipalities have been allowed to dump
reduced the amount of phosphates that municipalities are allowed to dump
reduces the amount of phosphates allowed for dumping by municipalities
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笔记：主要纠结于从句时态：
1.如果用一般过去时were也不如一般现在时are好，因为句意是持续的现在还在发生的
2.来自曼哈顿论坛的助教回答：
That said, there's a difference in meaning. Consider the following (correct) sentences:
When I was 10, my parents changed the time I go to bed.
When I was 10, my parents changed the time I went to bed.
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