Which of the following relations is not a function?
(2, 4), (-2, 2), (2, 1), (-8, 2)

(-8, 4), (2, 3), (-2, 1), (5, 2)

(5, 4), (-2, 2), (2, 1), (-8, 2)

(-2, 4), (2, 2), (5, 1), (-8, 5)