State which of the following sets of ordered pairs represent a function. Set A: (5, 2), (4, 3), (3, 4), (2, 5)
Set B: (-1, -6), (0, 2), (1, 2), (3, 6)
Set C: (2, 1), (4, 2), (2, 3), (8, 4)

a. Set C
b. Set B
c. Set A
d. Set A and Set B