单项选择题
A.The port on switch CAT1 is forwarding and sending BPDUs correctly.
B.The port on switch CAT1 is blocking and sending BPDUs correctly.
C.The port on switch CAT2 is forwarding and receiving BPDUs correctly.
D.The port on switch CAT2 is blocking and sending BPDUs correctly.
E.The port on switch CAT3 is forwarding and receiving BPDUs correctly.
F.The port on switch CAT3 is forwarding， sending， and receiving BPDUs correctly.
单项选择题 Refer to the exhibit. What does the command channel-group 1 mode desirable do？ （）
多项选择题 Refer to the exhibit. Initially， LinkA is connected and forwarding traffic. A new LinkB is then attached between SwitchA and HubA. Which two statements are true about the possible result of attaching the second link？（）
单项选择题 HowareSTPtimersandstatetransitionsaffectedwhenatopologychangeoccursinanSTPenvironment？（）
