Which two statements regarding the IS-IS DIS election process are true？ （）

• A、A priority of 0 will prevent a router from becoming a DIS.
• B、If the DIS becomes unavailable the backup DIS is promoted to DIS.
• C、Adding a router with a higher priority than the current DIS will result in the new router becoming DIS.
• D、Separate L1 and L2 election processes are held on a brodcast network.
• E、L1 routers on a broadcast network only establish adjacencies with the DIS.
• F、If there is a tie based on priority，the router whose attached interface has the lowest MAC address becomes the DIS.