Which types of multicast distribution tree can PIM-SM use?
A. Only shared tree rooted at the source
B. Only shared tree rooted at the RP
C. Only shortest path tree rooted at the RP
D. Shared tree rooted at the source and shortest path tree switchover
E. Shared tree rooted at the RP and shortest path tree switchover
F. Shared tree rooted at the first-hop router and shortest path tree rooted at the RP
