99 POINTS!!!!! FAST

Which set represents the domain of the function shown?

{(−3, 6), (0, 2), (4, 7), (11, 15)}

A. {(6, −3), (2, 0), (7, 4), (15, 11)}

B. {2, 6, 7, 15}

C. {−3, 0, 4, 11}

D. {−3, 0, 2, 4, 6, 7, 11, 15}

(P.S. The 99 points were obviously fake XD)