Which of the following relations is a function?
A.
(2, 1), (-2, 4), (-5, 1), (2, -5)

B.
(-5, 4), (-2, 6), (-5, 3), (7, 2)

C.
(-5, 1), (-2, -5), (2, 5), (7, 1)

D.
(-5, 1), (-2, 4), (2, -5), (-2, 6)