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