DCS系统中传递电信号的传输介质一般采用（）。
A.双绞线
B.同轴电缆
C.光导纤维
D.控制电缆
参考答案：B
What are they doing? They ____________.
A．take photos
B．are taking photo
C．take a photo
D．are taking photos
干辣根
