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