Which two statements are true about RPF checks in MSDP（Multicast Source Discovery Protocol）？（）

A.It prevents message looping，Session Advertisement（SA）messages must be RPF checked
B.RPF check should be done against the route to the Rendez-vous Point of the corresponding PIM-SM domain，which originated the SA
C.RPF checking Session Advertisement（SA）messages will cause message looping
D.RPF check should be done against the route to the source S of the corresponding PIM-SM domain