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