单项选择题
AportinaredundanttopologyiscurrentlyintheblockingstateandisnotreceivingBPDUs.Toensurethatthisportdoesnoterroneouslytransitiontotheforwardingstate，whichcommandshouldbeconfiguredtosatisfytherequirement？（）
A.Switch（config）#spanning-treeloopguarddefault
B.Switch（config-if）#spanning-treebdpufilter
C.Switch（config）#udldaggressive
D.Switch（config-if）#spanning-treebpduguard
A.Toensurethatthisportdoesnoterroneouslytransitiontotheforwardingstate，whichcommandshouldbeconfiguredtosatisfytherequirement？（）
A.Switch（config）#spanning-treeloopguarddefault
B.Switch（config-if）#spanning-treebdpufilter
C.Switch（config）#udldaggressive
D.Switch（config-if）#spanning-treebpduguard