题目内容

镜头的通光量以镜头的焦距和通光孔径的比值来衡量，以F为标记，每个镜头上均标有其最大的F值，通光量与F值的平方成正比关系，F值越大，则光圈越大。

A. 对
B. 错

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镜头的调整，1/3inch的镜头由于其有效成像面积小，不能用于1/2inch的摄像机，而1/2inch的镜头则可用于1/3inch的摄像机。

A. 对
B. 错

She _________English since she was a child.

A. learned
B. learning
C. learns
D. has been learning

I saw that she________at her homework at eleven last night.

A. was working
B. worked
C. works
D. has worked

He________trying to save a child in the earthquake.

A. was killed
B. is killed
C. has killed
D. killed