问题补充:
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
答案:
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。