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OG12 74请教
a 1972 agreement between canada and the united states reduced the amount of phosphates that municiplities had been allowd to dump into the great lake
A. reduced the amount of phosphates that municipaliteies had been allowed to dump
D.reduced the amount of phosophates that municipalities are allowed to dump
请问为什么不选A？ HAD BEEN ALLOWED这里为什么错呀 我理解是 过去在1972年前一直到1972BEEN ALLOWED的 为什么非要用ARE呢 |
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