单项选择题
A.Switch（config-if）#spanning-tree guard root
B.Switch（config-if）#spanning-tree portfast
C.Switch（config-if）#switchport mode trunk
D.Switch（config-if）#switchport mode access
单项选择题 A port in a redundant topology is currently in the blocking state and is not receiving BPDUs. To ensure that this port does not erroneously transition to the forwarding state， which command should be configured to satisfy the requirement？（）
单项选择题 Whichspanning-treecommandwouldcauseaPortFast-enabledinterfacetoloseitsPortFast-operationalstatusanddisableBPDUfilteringifitreceivesBPDUs？（）
单项选择题 Whichofthefollowingconditionsguaranteesthatabroadcaststormcannotoccur？（）