Which relation is a function?

A.x −2 0 0 2 4
y 4 3 4 4 6


B.x 3 5 7 10 14
y 9 6 9 2 3


C.x −3 2 2 4 6
y 2 1 8 5 3


D.x −6 −1 1 1 6
y 0 6 2 −3 4