Which set of ordered pairs represents a function? A. {(1, 2), (2, 3), (3, 2), (2, 1), (1, 0)} B. {(5, 1), (5, 2), (5, 3), (5, 4), (5, 5)} C. {(1, 4), (2, 4), (3, 4), (4, 3), (4, 2)} D. {(0, 7), (2, 7), (4, 7), (6, 7), (8, 7)}