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 tw o IP addresses.
• D、EIGRP cannot form neighbor relationship and exchange routing updates with a secondary address.