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