1. [单选题]下面有关交换机的描述中，正确的是（）
A. 所有交换机都支持VLAN功能
B. 交换机端口数量最多为48口
C. 交换机独占带宽
D. 交换机端口的最大速率为100Mbit/s
2. [单选题]Which one of the following characteristics is true regarding the use of hubs and switches?
A. Hubs can have their ports be configured with VLANs
B. Using hubs is costly with regard to bandwidth availability.
C. Switches can not forward broadcasts.
D. Switches are more efficient than hubs in processing frames.
E. Switches increase the number of collision domains in the network.
3. [单选题]路由器下，由一般用户模式进入特权用户模式的命令是：（）
A. enable
B. config
C. interface
D. router
