单项选择题
A.spanning-tree mode rapid-pvst
B.spanning-tree uplinkfast
C.spanning-tree backbonefast
D.spanning-tree mode mst
单项选择题 Why would a network administrator configure port security on a switch（）。
单项选择题 Hosts on the same VLAN can communicate with each other but are unable to communicate with hosts on different VLANs. What is needed to allow communication between VLANs（）。
单项选择题 There are no boot system commands in a router configuration in NVRAM.What is the fall back sequence that router will use to find an ios during reload？（）