Current Enterprise Networks Usually Use OSPF as the Routing Protocol

Current enterprise networks usually use OSPF as the routing protocol. What precautions are there when OSPF is used? (Choose four.)

A) Determine that the backbone area will not split.
B) Check whether secondary optimal routes exist on the network according to OSPF route selection rules.
C) Check whether all non-backbone areas are correctly and reliably connected to the backbone area.
D) Check the OSPF network topology and ensure that no loop exists when OSPF routes are being calculated.
E) Verify that OSPF costs can correctly demonstrate the actual bandwidth of links at more than 100 Mbit/s.