There was _____ I cared about how others may see me. Now I know how silly I was.

A．a time that

B．time that

C．time when

D．a time when

如果振荡器不起振，应先用万用表测量放大器的（）

A.电源

B.输入信号

C.静态工作点

D.输入阻抗