Which set of ordered pairs represents a function?
A. {(0,5), (2,5),(4,5), (6,5), (8,5)}
B. {(3, 1), (3, 2), (3, 3), (3, 4), (3,5)}
C. {(2,3), (3, 4), (4,3), (3, 2), (2, 1)}
D. {(1, 4), (2, 4), (3, 4), (4, 3), (4, 2)}