To establish eBGP peering using loopback interfaces as the BGP router ID, you need to specify the neighbor's loopback address with the remote-as command followed by setting the update source to the local router's loopback interface. The configuration provided in option A correctly sets up eBGP peering between R3 and R4 using their respective loopback addresses for BGP router ID. References: Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) v1.1