ISIS elects DIS in broadcast multiplexed access networks, and the following statement about DIS is correct? (Multiple choice)

ISIS elects DIS in broadcast multiplexed access networks, and the following statement about DIS is correct? (Multiple choice)
A . ISIS elects dis by comparing priorities, and mac addresses if the priorities are consistent
B . In a broadcast multiple access network, DIS sends Hello PDUs at three times the frequency
C . DIS guarantees database synchronization by periodically sending CSNP messages
D . DIS supports preemption function, after the new DIS preemption is successful, there is no need to flood any LSP packet

Answer: A,B,C