Refer to the exhibit.

An OSPF virtual link is configured between R4 and R3. Based upon the show command output,
why is the virtual-link down?

A.
Virtual links cannot transit area 0.

B.
The cost of the virtual link needs to be configured as 1.

C.
The timer intervals for virtual links need to be aggressive (2, 8, 8, and 1).

D.
The virtual interface VL1 is shut down.