An administrator types in the command router ospf 1 and receives the er ror message: "OSPF process 1 cannot start." (Output is omitted.) What should be done to correctly set up OSPF？（）

• A、Ensure that an interface has been configured with an IP address
• B、Ensure that IP classless is enabled
• C、Ensure that the interfaces can ping their directly connected neighbors
• D、Ensure that an interface has been configured with an IP address and is up