Which command do you enter on router R6 so that BGP supports multiple protocols?
A. R6(config-router)#no bgp default ipv4-unicast
B. R6(config-router-af)# bgp additional-paths install
C. R6(config-router)#bgp default ipv4-multicast
D. R6(config-router-af)#no bgp default ipv4-multicast
E. R6(config-router)#no address-family ipv4 unicast
A
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-mt/irg-15-mt-book/irg-sup-clns.html
Address Family Routing Information
By default, commands entered under the router bgp command apply to the IPv4 address family. This will continue to be the case unless you enter the no bgp default ipv4-unicast command as the first command under the router bgp command. The no bgp default ipv4-unicast command is configured on the router to disable the default behavior of the BGP routing process exchanging IPv4 addressing information with BGP neighbor routers.