1. [单选题]IP地址为：192.168.50.70，掩码为：255.255.255.248，则该IP地址所在子网的子网号为（）
A. 192.168.50.32
B. 192.168.80.64
C. 192.168.50.96
D. 192.168.50.71
2. [单选题]交换机工作在OSI七层模型的哪一层()
A. 物理层
B. 数据链路层(data link layer)
C. 网络层
D. 传输层
3. [单选题]路由器上“水平分割”的功能是：()
A. 分离端口
B. 阻止路由环路
C. 简化配置
D. 方便故障处理
4. [多选题]Which of the following statements correctly describe the differences between half-duplex and full-duplex Ethernet? (Select two answer choices.)
A. Full-duplex Ethernet uses CSMA/CD to prevent collisions.
B. Half-duplex Ethernet uses a loopback circuit to detect collisions.
C. A full-duplex Ethernet card allows 20Mbps for data transmission.
D. Full-duplex Ethernet makes use of two pairs of wires for data.
E. An Ethernet hub can operate both half and full duplex simultaneously.
5. [单选题]下列命令中，无法正确执行的是（）
A. Router(config)show run
B. Routerping 127.0.0.1
C. Router(config)hostname cisco
D. Routerreload
