The following sets of ordered pairs represent relations from the set X to the set Y. Which one is a function?

A (3, 4), (3, 5), (3, 6), (3, 7)
B (2, 5), (2, 8), (3, 7), (3, 9)
C (1, -1), (0, 0), (1, 1), (4, 2)
D (0, 0), (1, 1), (4, 2), (9, 3)