Which of the following is not a function?
O A. {(1,2), (2,2), (3,2), (4,2)}
B. {(1,2), (9,-3), (-3,-1), (8,2)}
C. {(1,2), (2,3), (3,4), (4,5)}
D. {(1,2), (-2,3), (1,3), (-2,2)}