Which set of ordered pairs does not represent a function?

{(7, -5), (-5, -2), (8, –9), (-9,0)}

{(-3,0), (0, -5), (6,-2), (1, -2)}

{(6, -6), (-9,2), (6, -1), (-8, -9)}

{(7,3), (2, –6), (5, –7), (0, – 7)}