You are troubleshooting an OSPF problem where external routes are not showing up in the OSPF database. Which two options a re valid checks that should be performed first to verify proper OSPF operation?（）

• A、Are the ASBRs trying to redistribute the external routes into a totally stubby area?
• B、Are the ABRs configured with stubby areas?
• C、Is the subnets keyword being used with the redistribution command?
• D、Is backbone area (area 0) contiguous?
• E、Is the CPU utilization of the routers high?