Refer to the exhibit. BGP-4 routing to the Internet，in normal behavior，may create asymmetrical routing for different prefixes. The BGP routing table indicates that traffic should follow the paths indicated in the exhibit，but packets are not going further than the border router in AS 4. What could be the cause of this problem？（）

A.TCP Intercept is configured in AS 4.
B.Unicast Reverse Path Forwarding is configured in loose mode in this router.
C.Packets may be leaving AS 1 without the BGP routing flag set to 1.
D.Unicast Reverse Path Forwarding is configured in strict mode in this router.
E.There is a missing Unicast Reverse Path Forwarding configuration.