Explain the function of a rendezvous point ?
A RP is the focal point for multicast traffic. Traffic is forward to the RP from multicast sources. The RP then forwards traffic to multicast receivers.
What is the purpose of the interface command ip multicast spares-dense-mode ?
Used with PIMSM Auto-RP and version 2. if the RPs fail, the router reverts to dense mode.
Describe the operation of Anycast RP.

Two or more RPs are configured with the same IP address. The IP addresses of the RPs are advertised using a unicast IP routing protocol. Each multicast router chooses the closet RP. If an RP fails, the routers switch to the next nearest RP after the unicast ip routing protocol converges. The MSDP is used between RPs to exchange active multicast source information.

What protocols do switches use to prevent the broadcasting of multicast traffic ?

CGMP and IGMP Snooping.

Why are the Cisco multicast routing protocols referred to as protocol independent ?
Multicast forwarding decisions are based on the entries in the unicast IP routing table. Multicast is not dependent on how the unicast IP routing table was built; you cans use any dynamic interior routing protocol, static routes, or a combination of the two.