Had your father seen the doctor earlier, he ____.

A．would have died

B．would not have died

C．would not die

D．has not died

无线电广播信号的发射由广播电台完成。话筒把播音员的_______信号转换成音频电信号，然后用调制器把音频电信号加载到高频电流上，再通过________发射到空中。