正解:C
In the given scenario, Cisco IOS routers R1 and R2 can form an OSPF neighborship on interface Gi0/0 by ensuring that the interface is not set as passive and by configuring the OSPF network command on R1. In Option C, R2 has been configured with "passive-interface Gi0/0" under the OSPF routing process, which means OSPF neighbor relationships won't be formed on thisinterface. However, on R1, "no passive-interface Gi0/0" is configured ensuring that OSPF hello packets are exchanged allowing for neighbor formation.
Additionally, the "network" command is used to enable OSPF on specified interfaces belonging to the mentioned network.