Which two statements are true about Internet Group Management Protocol (IGMP) snooping?（）

A. IGMP snooping and Cisco Group Membership Protocol (CGMP) can be used simultaneously on a switch.
B. IGMP snooping a nd Cisco Group Membership Protocol (CGMP) were developed to help Layer 3 switches make intelligent forwarding decisions on their own.
C. IGMP snooping examines IGMP join/leave messages so that multicast traffic is forwarded only to hosts that sent an IG MP message toward the router.
D. IGMP snooping is an IP multicast constraining mechanism for Layer 2 switches.
E. IGMP snooping is enabled with the ip multicast - routing global configuration command.