Refer to the exhibit. Routers R1 and R2 are directly connected via their serial interfaces and are both running the EIGRP routing protocol. R1 and R2 can ping the directly connected serial interface of their neighbor, but they cannot form an EIGRP neighbor adjacency.
What action should be taken to solve this problem?
Enable the serial interfaces of both routers.
Configure EIGRP to send periodic updates.
Configure the same hello interval between the routers.
Configure both routers with the same EIGRP process ID.