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