In PIM-SM what control plane signaling must a multicast source perform before it begins to send multicasttraffic to a group？（）
- AThe source must send a PIM Register message to the rendezvous point （RP）.
- BThe source must first join the multicast group using IGMP before sending.
- CThe source must perform a Request to Send （RTS） and Clear to Send （CTS） handshake with the PIM designated router （DR）.
- DNo control plane signaling needs to be performed； the source can simply begin sending on the local subnet.