Which of the following lists of ordered pairs is a function?
A) (1,1), (2,2), (3,1), (3,2)
B) (-2,3), (2,4), (-3,6), (3,7)
C) (0,3), (-1,4), (1,6), (-1,7)
D) (2,5), (3,-4), (4,7), (2,2)