Which set of ordered pairs represents a function?
a.
(2, 5), (1, 6), (0, 5), (1, 10)
b.
(5, 4), (4, 5), (1, 2), (1, 4)
c.
(0, 0), (1, 1), (2, 0), (3, 3)
d.
(2, 1), (3, 1), (5, 1), (5, 4)