Which set of ordered pairs respresents a function? a. {(2, -2), (1, 5), (-2, 2), (1, -3), (8, -1)} b. {(3, -1), (7, 1), (-6, -1), (9, 1), (2, -1)} c. {(6, 8), (5, 2), (-2, -5), (1, -3), (-2, 9)} d. {(-3, 1), (6, 3), (-3, 2), (-3, -3), (1, -1)}