Question

Which set of ordered pairs represents a function?
A. (3,3), (3, 2), (3,1), (3,0)
B. (1,2), (7,9), (5,8), (1,7)
C. (5,4), (6,3), (7,2), (8,1)}
D. (7,8), (8,7), (7,9), (9,7)