单项选择题
Acknowledgements, sequencing, and flow control are characteristics of which OSI layer（）。
A.Layer2 B.Layer3 C.Layer4 D.Layer5 E.Layer6 F.Layer7
单项选择题 When a new trunk link is configured on an IOS based switch, which VLANs are allowed over the link（）。
单项选择题 What is one benefit of PVST+?（）
单项选择题 When a router is connected to a Frame Relay WAN link using a serial DTE interface, how is the interface clock rate determined（）。
