What is the function of the ip pim sparse- dense- mode command?

A.
Allows the router to perform RPF checks

B.
Enables PIM- SM if an RP is detected, if no RP is detected, PIM- DM is used

C.
Enables bidirectional multicast routing

D.
Enables PIM- DM if an RP is detected, if no RP is detected, PIM- SM is used