PLEASEEE HELPPP!!!!

Which of the following relations is NOT a function?
A. ((0, 1), (1, 1), (2, 1), (3, 1))
B. {(0, 1), (0.2), (0, 3), (0,4)}
C. (0,0), (3, 4), (5, 6), (8, 9)}
D. {(0, 0), (2, 2), (4,4), (6, 6))