Which of the following statements is correct regarding PIM Sparse Mode operations？（）

• A、It does not support all underlying unicast routing protocols like GBP
• B、It supports shared trees only assuming all hosts want the multicast traffic
• C、Receivers are registered with RP by their first-hop router
• D、Receivers are joinedto the Shared Tree（rooted the rp ）by their local Designated Router（DR）
• E、From the RP，traffic flows down a Source Tree to each receiver