What did he do

A．He telephoned me.

B．He picked up the phone.

C．He put the receiver down.

D．He put my hanger up.

沉筒式液位计的沉筒液位变送器是用扭力管将沉简的位移转换为心轴的（），经一系列机械传动后再通过（）变送器变成电信号。