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
网友回答
A. had studied
B. would study
C. studied
(答案→)D. have studied
解析：考查时态。根据时间状语in the past twelve months在过去的12个月，用现在完成时，故选D。