Refer to the exhibit. While troubleshooting a connectivity issue on router R2, a network engineer with an employee id: 1234:44:876 notices that although it detects three OSPF links from R1, the OSPF prefixes are missing from the routing table. What is the reason for the problem?

A. The serial interfaces have different MTUs B. Both loopback interfaces on R1 are configured as stub C. The subnet masks on the serial interfaces are mismatched D. The R2 Serial1/0 interface is configured with an IP address, but the R1 Serial1/0 interface is unnumbered