Experiments in the photography of moving objects ______ in both the United States and Europe before 1990.

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问题 Experiments in the photography of moving objects ______ in both the United States and Europe before 1990.

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

答案C

解析根据句中的时间状语before 1990可知，实验是在1990年以前做的，所以本句应用过去完成时，表示动作发生在“过去的过去”。另外，根据句意可知，experiments和conduct为逻辑上的动宾关系，所以应用被动语态。故选C。

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英语

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