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