2 . In the past twelve months the research members ______ the effectiveness of many materials in a home building . A . had studied B . would study C . studied D . have studied请说明一下，谢

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2 . In the past twelve months the research members ______ the effectiveness of many materials in a home building . A . had studied B . would study C . studied D . have studied请说明一下，谢
2 . In the past twelve months the research members ______ the effectiveness of many materials in a home building .
A . had studied B . would study C . studied D . have studied
请说明一下，谢

2 . In the past twelve months the research members ______ the effectiveness of many materials in a home building . A . had studied B . would study C . studied D . have studied请说明一下，谢
D
因为是in the past twelve months
而且学习这个动作已经完成了
所以用过去完成时

C studied

在过去的多少时间里，常用完成时。所以，选D。

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