Which set of ordered pairs represents a function?
O {(-1,-8), (-7, -9), (-1,-6), (0, -7)}
○ {(-4, 6), (-1, 5), (3, −5), (9,6)}
○ {(2,7), (4,4), (2, 3), (9, -1)}
○ {(-4,-4), (-4, 9), (6, -2), (-9,-6)}