which event triggers the creation of a shortest-path tree?

When using PIM-SM in SSM mode, which event triggers the creation of a shortest-path tree?

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

B.
An IGMPv3 report received at the receiver’s designated router (DR).

C.
Multicast traffic received at the rendezvous point (RP).

D.
An IGMPv3 report received at the source’s designated router (DR).