Which of the following relations is a function?
OA. (2.0), (-1, 3), (7, 1), (-1,5)
OB. (2,4), (-1, 2), (7, 1), (-8, 2)
OC. (7,1),(-1, 4), (2, 1), (7, 2)
OD. (2, 4), (-1, 6), (2, 3), (-8, 2)