For which list of ordered pairs is y a function of x?
A.(7,-7), (-7,-5), (-7,-3), (-7,-1)
B.(-3, 9), (0, 0), (0, 9), (3, 12)
C. (6, 8), (10, 8), (15,-7), (16, 0)
D. (11, -2), (12, 1), (13,-4), (13, 9)