Would you please ______ the light ?  I can’t see much clearly . It is getting dark .

A．switch off

B．switch on

C．turn off

D．take on

天线放大器如果距离振子太远，则会使电缆损耗电平增大和( )。

A．产生回馈

B．增益低

C．信噪比变坏

D．抗干扰能力弱