In which set of points is y a function of x?
A {(2, 4), (4,16),(5, 25), (6, 36)}
B{(4,2), (4,-2), (16,4), (16,-4)}
C{(2, 1), (2,0), (1, -1), (3, 1)}
D{ (2, 3), (1,3), (0, 3), (0, 2)}