集线器工作在OSI模型的物理层普通交换机工作在OSI模型的（）层。
A、物理
B、数据链路
C、网络
D、传输
参考答案：B
The air company going from bad to worse, the workers____________ hardly enough to make a living.
A．are paid
B．are paying
C．have paid
D．paid
