What is the mechanism that is used to allocate MAC addresses that are assigned to the VDC for the system MAC address？（）   

• A、 NX-OS uses a random MAC address from the IEEE OUI block that is assigned to Cisco.
• B、 The VDC system MAC is pulled from the active supervisor and concatenated through a hash to ensure uniqueness.
• C、 NX-OS uses a value that is based on a range that is assigned to the SPROM of the system backplane.
• D、 The VDC system MAC is based on a range that is allocated to the first line card that is installed in the switch.