Which set of ordered pairs does not represent a function?
A{(-4,3), (8,3), (-2, 3), (7,7)}
B{(-2,-5), (0, -2), (9,9), (2,1)}
C{(9,3), (5, 4), (3, 3), (-6,3)}
D{(6,1), (8,2), (-4,5), (6,3)}​