The Voice of China has set up a stage        some people can achieve their dreams．

A．which

B．where

C．that

D．when

关于变压器下列正确的说法是（）。

A、变压器用来变换电压

B、变压器是一种静止的电气设备

C、变压器可以变换阻抗

D、变压器可以改变频率