正解:C
The OSPF neighborship fails between two routers due to an MTU mismatch. In OSPF, for a neighborship to be established, the MTU size on the interfaces that connect neighboring routers should match. If there is a mismatch in the MTU size, OSPF adjacency will not form. In the provided exhibit, it can be observed from the log messages that there is an MTU mismatch error (mtu 9100 state EXSTART), indicating that this is the reason for OSPF neighborship failure. References := Cisco - Implementing and Operating Cisco Service Provider Network Core Technologies