按照OSI模型，HUB工作在第几层？（）
A、物理层
B、数据链路层
B、IP层
D、应用层
参考答案：A
Look, the lights in the room don’t . Someone must forget .
A．put out; going them out
B．be out; put them out
C．go out; to put them out
D．go out; putting them out
为什么摇测电缆绝缘时，先要对电缆进行放电？
