With What Techniques Is Grandmaster Flash Credited in Rap

With what techniques is Grandmaster Flash credited in rap?

A) Flash was notorious for simply copying other rappers' styles.
B) Flash began the rap music tradition of using female backup singers.
C) He is credited with the technique of scratching and combining records on two turntables to produce a unique song.
D) He is generally credited with beginning the style known as "gangsta rap."