Which two statements concerning STP state changes are true？ （）

• 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.