Which relations represent a function?

A.
(16, 14)
(14, −12 )
(9, 11)
(10, 14)

B.
(10, 8)
(7, 9 )
(9, 13)
(8, 5)

C.
(18, 24)
(16, 10 )
(5, 13)
(18, 14)

D.
(14, 12)
(10, 12 )
(−13, 7)
(11, 15)