What could be the cause of the problem?

Refer to the exhibit. EIGRP has been configured on routers R1 and R2. However, R1 does
not show R2 as a neighbor and does not accept routing updates from R2. What could be the
cause of the problem?

A.
The no auto-summary command has not been issued under the EIGRP process on both
routers.

B.
Interface E0 on router R1 has not been configured with a secondary IP address of
10.1.2.1/24.

C.
EIGRP cannot exchange routing updates with a neighbor’s router interface that is
configured with two IP addresses.

D.
EIGRP cannot form neighbor relationship and exchange routing updates with a secondary
address.