which two events trigger the creation of a shortest-path tree?

When using PIM-SM in ASM mode, which two events trigger the creation of a shortest-path tree?
(Choose two.)

A.
Multicast traffic received at the receiver’s designated router (DR).

B.
PIM join received at the receiver’s designated router (DR).

C.
PIM join received at the source designated router (DR).

D.
PIM registers received by the rendezvous point (RP).

Explanation: