Refer to the exhibit. Why does the multicast traffic go via R21 only, instead of using all the three ECMP links? 

Answer options:

A. By default, IP multicast chooses the interface that has the PM neighbor with the highest IP address as the incoming interface and then sends prunes to PIM neighbors on the other links
B. R21 has the shortest returned path to the source as the output of the show ip rpf 111.111.111.111 command shows
C. IP multicast load balances traffic only per flow-basis, at the time the engineer performed the command the path chosen was via R21. Next time the show command is performed, it will show an alternative path
D. This behavior is not normal. The multicast traffic must be load-shared between all available paths

A