555定时器构成的多谐振荡电路的脉冲频率由（）决定。

A、输入信号

B、输出信号

C、电路充放电电阻及电容

D、555定时器结构

( ) Mike ( ) his sister are interested in Chinese.

A．Either, or

B．Neither, nor

C．Not, but,

D．Both, and