【题目】Experiments of this kind____ in both the U.S. and Europe well before the Second World War.
A. have conducted B. have been conducted
C. had conducted D. had been conducted
在线课程【答案】D
【解析】试题分析：考查时态。句意：在二战以前，这种实验已经在美国和欧洲进行了无数次。experiments与conduct是动宾关系，应该用被动，排除A、C；根据“before the Second World Wall”可知，应该用过去完成时，故选D。