Which command must be applied to R2 for an OSPF neighborship to form?

Refer to the Exhibit.

Which command must be applied to R2 for an OSPF neighborship to form?
A . network 20.1.1.2.0.0.0.0 area 0
B . network 20.1.1.2 255.255.0.0. area 0
C . network 20.1.1.2.0.0.255.255 area 0
D . network 20.1.1.2 255.255.255 area 0

Answer: A

Explanation:

The Dnetwork 20.0.0.0 0.0.0.255 area 0‖ command on R2 did not cover the IP address of Fa1/1 interface of R2 so OSPF did not run on this interface. Therefore we have to use the command Dnetwork 20.1.1.2 0.0.255.255 area 0‖ to turn on OSPF on this interface.

Note: The command Dnetwork 20.1.1.2 0.0.255.255 area 0‖ can be used too so this answer is also correct but answer C is the best answer here.

The Dnetwork 0.0.0.0 255.255.255.255 area 0‖ command on R1 will run OSPF on all active