Which set of ordered pairs represents y as a function of X? a{(-9, 2), (0, 6), (1, -2), (-3, 6)} b{(-1,0), (4, 3), (-7, -3), (-1, -8)} c{(3, 2), (-4,-2), (3, 1), (-4,1)} d{(5, 4), (2, 3), (1, 1), (2,4)}​