A. The sequence numbers are checked, and if the LSA is val id it is entered into the topology database.
B. The LSA is placed in the topological database and an acknowledgement is sent to the transmitting router.
C. The LSA is dropped and a message is sent to the transmitting router.
D. The LSA is flooded imme diately out of all the OSPF interfaces, except the interface from which the LSA was received.

A. The network domain, when divided into areas, allows for the use of both IANA classful addressing and private addressing.
B. The use of multiple areas allows for the use of prioritization.
C. All computation is kept within the area, with minimum communication between the areas,allowing the network to scale to  larger sizes.
D. It is easier to implement security.