Experiments of this kind____in both the U.S.and Europe well before the World War.A.have conducted B.have been conductedC.had conducted D.had been conducted

Experiments of this kind____in both the U.S.and Europe well before the World War.A.have conducted B.have been conductedC.had conducted D.had been conducted
Experiments of this kind____in both the U.S.and Europe well before the World War.
A.have conducted B.have been conducted
C.had conducted D.had been conducted

Experiments of this kind____in both the U.S.and Europe well before the World War.A.have conducted B.have been conductedC.had conducted D.had been conducted
Experiments of this kind____in both the U.S.and Europe well before the World War.
A.have conducted B.have been conducted
C.had conducted D.had been conducted
句子大意：在世界大战之前这种实验已经在美国和欧洲两地进行的很好了.
通过时间状语“before the World War”可判断是过去的时间,所以可排除AB!
再有就是Experiments与conduct之间是被动关系,所以选D是对的!

D.had been conducted
过去发生的事，所以过去完成时
又是被动，所以D

D