Which two statements are true when the extended system ID feature is enabled？ （）

• A、The BID is made up of the bridge priority value（two bytes） and bridge MAC address （six bytes）.
• B、The BID is made up of the bridge priority （four bits）， the system ID （12 bits）， and a bridge MAC address （48 bits）.
• C、The BID is made up of the system ID （six bytes） and bridge priority value （two bytes）.
• D、The system ID value is the VLAN ID （VID）.
• E、The system ID value is a unique MAC address allocated from a pool of MAC addresses assigned to the switch or module.
• F、The system ID value is a hex number used to measure the preference of a bridge in the spanning-tree algorithm.