顶焦度计数值不稳时的维修方法为取下镜片支座，（）。

A、用嘴吹净光学零件表面灰尘

B、用脱脂棉蘸乙醇擦拭光学零件

C、用脱脂棉蘸生理盐水擦拭

D、其他方法

Between 1897 and 1919 at least 29 motion pictures in which artificial beings were portrayed （）。

A. had produced

B. have been produced

C. would have produced

D. had been produced