What causes this behavior?

You execute the operational-mode command show ospf neighbor and notice that one neighbor relationship remains in the exStart state. What causes this behavior?

A.
The area IDs do not match on each end of the link.

B.
The authentication parameters do not match on each end of the link.

C.
The dead interval does not match on each end of the link.

D.
The MTU does not match on each end of the link.