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.

A. Do not use or internally advertise a route until the route is lear ned from a source other than BGP.
B. Do not use or advertise a route until the route is learned from a BGP peer.
C. Do not use or advertise routes marked PARTIAL.
D. Wait until a CONFIRM message is received before using routes from BGP neighbors.