问题：

[单选] What technique should be used on BGP edge routers to prevent a multi - homed autonomous system from becoming a trans it system?（）

A . Advertise with a high MED value all networks that are discovered via external BGP.
B . Set the no - export community attribute on all networks that are advertised externally.
C . Remove the AS - Path information on all routes in the BGP table pr ior to advertising externally.
D . Set the origin code to incomplete for all networks that are discovered via external BGP.
E . Only advertise networks externally if they have been discovered via internal BGP.
F . Use an outgoing distribution list to filte r all networks not originating from inside the autonomous system.