PLEASE HELP ASAP!! WILL MARK BRAINLEST!!!!!

Which of the following represents a function?
A. (-5, 6), (-5, 6), (-5, -6), (-5, -6)
B. (5, 1), (5, 2), (5, 3), (5, 4)
C. (3, 9), (-7, 1), (6, 12), (-3, -9)
D. (8, 3), (8, 3), (-8, -3), (-8, -3)