为了稳定放大器的静态工作点，在放大器中常采用（）。
A.负反馈电路
B.正反馈电路
C.混合反馈电路
参考答案：A
—May I speak to Mr Wang, please?
—Sorry, you can't. He _ Shanghai. Can I take a message? [ ]
A. has been to
B. was in
C. has gone to
D. was at
光圈与快门速度的调整是根据相机所预设的相当感光度以及被拍摄景物的亮度所决定的。为了要控制动体的影像清晰度则应该调整光圈。( )
