Which relation is NOT a function?
O {(-2, 2), (-1, 1), (0, 0), (1, 1)}
O {(-2,4), (-1, 5), (1, 7), (2, 8)}
O {(-6,3), (-4, 0), (0, 0), (-6, -1)}
O {(-4, 1), (-2, 1), (2, 1), (4. 1)}