Which two statements concerning STP state changes are true？ （）
- AUpon bootup，a port transitions from blocking to forwarding because it assumes itself as root.
- BUpon bootup，a port transitions from blocking to listening because it assumes itself as root.
- CUpon bootup，a port transitions from listening to forwarding because it assumes itself as root.
- DIf a forwarding port receives no BPDUs by the max_age time limit， it will transition to listening.
- EIf a forwarding port receives an inferior BPDU， it will transition to listening.
- FIf a blocked port receives no BPDUs by the max_age time limit， it will transition to listening.