题目内容
（请给出正确答案）
[主观题]
Experiments in the photography of moving objects______in both the United States and Europe
well before 1990.
A．have been conducting
B．were conducting
C．had been conducted
D．are conducted
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A．信托业务
B．融资租赁业务
C．信用卡业务
D．承诺业务
