Which two OSPF network scenarios require OSPF virtual link configuration? (Choose two.)
A . to connect an OSPF non-backbone area to area 0 through another non-backbone area
B . to connect an NSSA area to an external routing domain
C . to connect two parts of a partitioned backbone area through a non-backbone area
D . to enable route leaking from Level 2 into Level 1
E . to enable route leaking from Level 1 into Level 2
F . to enable OSPF traffic engineering
Answer: A,C