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