you may have , you should gather your courage to face the challenge .

A．However serious a problem

B．Whatever serious a problem

C．However a serious problem

D．No matter how a serious

高频开关电源采用脉宽调制（PWM）方式，其开关频率一般在30—500KHz范围内，如果开关频率再提高，就会（）。

A、对外发射，影响通信设备

B、两组开关管来不及相互转换

C、开关损耗随之增加，效率反而下降