问题补充:
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
答案:
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。