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：句意：在二次世界大战之前这种实验在欧洲和美国进行得很好。the Second World War发生在过去，又因为before在…….之前，所以表示的是过去的过去，Experiments of this kind与conduct是被动关系，故用被动语态。根据句意故选D。