问题：

[多选] 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.