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