问题：

[单选] 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