单选题
Experiments in the photography of moving objects ______ in both the United States and Europe before 1990.
A、
have been conducting
B、
were conducting
C、
had been conducted
D、
are conducted
【正确答案】
C
【答案解析】
[解析] 根据句中时间状语“before 1990”可知，实验是在1990年之前做的，因此本句话应该用过去完成时。根据句意可知，experiments和conduct为动宾关系，所以应用被动语态。故选C。
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