Experiments of this kind in both the U．S and Europe well before the Second World War．
A. had conducted
B. have conducted
C. have been conducted
Dhad been conducted
网友回答
A. had conducted
B. have conducted
C. have been conducted
(答案→)D. had been conducted
解析：
试题分析: 考查动词时态。根据before the Second World War可知此处是指过去的过去，应该用过去完成时；而experiment和conduct是被动关系，所以用过去完成时的被动形式,故答案选D。句意：二战前就在美国和欧洲进行过这种实验。