1. [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.
2. [多选题]请选出交换机处理帧的三种模式：()
A. 直通模式
B. 存储转发模式
C. 侦测模式
D. 分段模式
E. 阻塞模式
3. [单选题]介质工作在OSI的哪一层（）
A. 物理层
B. 数据链路层
C. 网络层
D. 传输层
