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.