Experiments in the photography of moving objects______in both the United States and Europe well before 1990.

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问题 Experiments in the photography of moving objects______in both the United States and Europe well before 1990.

选项 A、have been conducting
B、were conducting
C、had been conducted
D、are conducted

答案C

解析 本题是对基本时态和语态的考查。实验是被实施的,所以本题中要用被动语态,其次实验发生在1990年之前,已经是过去完成的事情,因此要用过去完成时,结合选项可知,本题的答案为C。
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