可控硅元件由关断变为导通时，控制极（）作用。
A、仍有
B、没有
C、有时有
参考答案：C
If you keep on, you'll succeed ________.[ ]
A. in time
B. at one time
C. at the same time
D. on time
It was intolerate to_____the book.
A．part from
B．say hello to
C．part with
D．separate from
