A、Upon bootup，a port transitions from blocking to forwarding because it assumes itself as root.

B、Upon bootup，a port transitions from blocking to listening because it assumes itself as root.

C、Upon bootup，a port transitions from listening to forwarding because it assumes itself as root.

D、If a forwarding port receives no BPDUs by the max_age time limit， it will transition to listening.

E、If a forwarding port receives an inferior BPDU， it will transition to listening.

F、If a blocked port receives no BPDUs by the max_age time limit， it will transition to listening.