What can cause two OSPF neighbors to be stuck in the EXSTART state?

What can cause two OSPF neighbors to be stuck in the EXSTART state?
A . There is a low bandwidth connection between neighbors.
B . The neighbors have different MTU settings.
C . The OSPF interfaces are in a passive state.
D . There is only layer one connectivity between neighbors.

Answer: B

Explanation:

Neighbors Stuck in Exstart/Exchange State

The problem occurs most frequently when attempting to run OSPF between a Cisco router and another vendor’s router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces don’t match. If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the neighboring router ignores the packet.0 When this problem occurs, the output of the show ip ospf neighbor command displays output similar that shown below:

router-6# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface