Which of the following relations is a function?
A.
(5, 10), (-8, 2), (-1, 8), (-5, 10)

B.
(10, 5), (2, -8), (8, -1), (10, -5)

C.
(5, 10), (-8, 2), (-1, 8), (-1, -5)

D.
(-1, 10), (-8, 2), (-1, 8), (-8, -5)