They        have arrived at lunchtime, but their flight was delayed.

A．will

B．can

C．must

D．should

限幅器用来限制话音信号的最大值，使进入调制器、放大器等电路的话音信号最大值，不超出其（），保证发信支路不过负荷。

A.线性范围

B.电压范围

C.功率范围