what is the cause of this problem?（）

• A、The OSPF area is not configured properly.
• B、The priority on R1 should be set higher.
• C、The cost on R1 should be set higher.
• D、The hello and dead timers are not configured properly.
• E、A backup designated router needs to be added to the network.
• F、The OSPF process ID numbers must match.