Which relation is not a function?

A(2,9), (-1,-5), (1,5), (5,0), (12, 3)
B. (-3, 1), (6,2), (8,3), (6,4), (3, 5)
C. (5, 1), (4,2), (3, 3), (2, 4), (1,5)
D. (7,2), (5,3), (3, 4), (1,5),(-1, 6)