How can this requirements be accomplished?

Service providers that implement MPLS Inter-AS Option B must ensure that the ASBRs between each provider learn all VPNv4 routers from both providers.

How can this requirements be accomplished?
A . Ensure that each ASBR is configured for all VRFs from within its own provider backbone
B . Configure each ASBR to retain route targets for all VPNv-4 learned routes
C . Configure the VRFs form the connecting provider in order to learn route targets on each ASBR
D . Ensure that LDP is conjured between each ASBR for label exchange on all VRFs

Answer: B