问题详情：
Experiment of this kind________in both the U．S. and Europe well before the Second World War.
A. have conducted B. have been conducted
C. had conducted D. had been conducted
【回答】
D 考查动词时态和语态。主语experiment与conduct构成动宾关系，谓语使用被动形式。before the Second World War是过去的过去，故用过去完成时。
知识点：过去完成时及其被动式
题型：选择题
