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