Which of the following relations is a function?
A.
(6, 10), (-9, 2), (-1, 7), (-5, 10)

B.
(-1, 10), (-9, 2), (-1, 7), (-9, -5)

C.
(10, 6), (2, -9), (7, -1), (10, -5)

D.
(6, 10), (-9, 2), (-1, 7), (-1, -5)