根据下图，图中的拓扑中存在多少个广播域？（）

A.lowest port MAC address
B.port priority number and MAC address
C.VTP revision number
D.highest port priority number
E.path cost

A.protecting a server frome unauthorized acces
B.controlling path selection，based on the route metric
C.reducing router CPU utilization
D.filterring packets that are passing through a router

A.Enable VTP pruning
B.From privileged mode，erase the startup configuration file，then reload.
C.From privileged mode，erase the vlandate file，then reload.
D.Cycle the switch power.