What set of ordered pairs is a not a function?

A. (1, 4), (2, 3), (3, 2), (4, 3)
B. (2, 3), (3, 2), (4, 4), (5, 2)
C. (-2, 3), (4, 1), (2, -1), (1, 5)
D. (-2, 3), (1, 4) (-2, -1), (1, 5)​