How was standard BGP modified to allow it to carry routing information for VPRNs?

A. By using the MED attribute to carry the OSPF metric.
B. By defining Extended Communities for use as the Route Target
C. By using the Cluster List attribute to carry the network prefix

D. By defining support for the VPN-IPv4 address family

E. By adding an additional field to the BGP Update to carry the VPRN label