Which relation is a function?

Question

(Points : 1)
A.(1, 2), (1, 5), (1, -1), (1, 4)}

B. {(8, -1), (2, -1), (3, 8), (2, 5}

C. {(-3, 4), (-2, 5), (0, 9), (0, 12)}

D. {(7, 12), (1, -5), (3, -10), (2, -5)}

Is its C :P?