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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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1.had been allowed to dump表示过去已经被倒掉的量，已经被倒了，就不能减少了，过去的事实不能被改变
2.订立法律条文 修改的肯定是 从订立点开始 之后生效的东西，即：1972年的法律不能减少城市在这之前的倾倒量。
法规内容的时态 应和订立点相同（were）或者比订立点晚（are）
3.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
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