Refer to the e xhibit. It is desired to set up a BGP neighbor relationship between routers R1 and R4. BGP packets between them could travel through R2 or R3. What is the simplest configuration that will allow for failover?（）

• A、Configure BGP n eighbor relationships between all interfaces on R1 and R4.
• B、Install a direct connection between R1 and R4.
• C、Configure loopback interfaces on R1 and R4 to provide the update source address for BGP packets.
• D、Configure only one neighbor relationship between R1's 192.168.1.2 interface and R4's 172.16.10.2 interface.