Which relation is also a function?

A.
B.
x y
C.
A dot plot graph shows on a coordinate plane passes through (4, minus 8), (2, minus 4), (2, minus 3), (1, minus 1), (0, 1), (minus 1, 2), (minus 1, 4), (minus 3, 5), and (minus 4, 7)
D.
x y