Which relation IS a function? A.{(3, -2), (5, 1), (1, -1), (4, 4), (5, 4)} B.{(2, 3), (2, 2), (3, 4), (4, 3), (5, 0)} C.{(1, 5), (2, 4), (3, 7), (2, 2), (1, -1)} D.{(3, 3), (2, 3), (1, 3), (0, 3), (-1, 3)}