Which would most likely cause this problem?

This question is about the formation of OSPF adjacency. An OSPF adjacency will not form correctly across a point-to-point link in the same area. Which would most likely cause this problem?

A.
Each interface has a different OSPF cost.

B.
Each interface is configured with secondary addresses as well as primary addresses.

C.
Each interface has a different MTU size.

D.
Each interface is configured with the ip unnumbered loopback 0 command.