Experiments of this kind   in both the U．S．a(chǎn)nd Europe well before the Second World War．
A．have conductedB．have been conducted
C．had conductedD．had been conducted
D
本題考查時(shí)態(tài)。根據(jù)句中時(shí)間狀語(yǔ)before the Second World War可知用過(guò)去完成時(shí)，由于experiments與conduct為被動(dòng)，故選D。
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