What are some of the essential elements of R&B?
A．The lyrics are about sad subjects, and the singers usually sing a lots of runs
B．The singers are black, and the songs are usually about love
C．The lyrics are about struggle and triumph in relationships, and the style of R&B is constantly changing because of influence from other types of music, creating many sub-genres
D．The rhythm is on the backbeat, and the singers usually rap instead of sing