—I wonder if you are still an employee in that small company?

—Oh, I ______, but now I’m a public servant in a government department.

A．used to be

B．have to be

C．used to

D．did

为了提高三极管的开关速度，可以（）。

A.增大工作电流

B.防止进入深饱和状态

C.减小基极电流

D.以上都正确