Which of the Following Are Differences Between PIM-SM and PIM-DM

Which of the following are differences between PIM-SM and PIM-DM?

A) PIM-SM has RPTs and SPTs but PIM-DM has only RPTs
B) BSRs/RPs exist only on a PIM-SM network, not on a PIM-DM network
C) PIM-SM is applicable to a network with few receivers; PIM-DM is applicable to a network with a larger number of receivers  
D) Whether in PIM-SM or PIM-DM mode, receiver hosts must join multicast groups through IGMP