Which sets of ordered pairs designate a function?
A) (2,3), (3,4), (4,5), (5,6).
B) (1,1), (-1,1), (2,4), (-2,4).
C) (0,0), (4,2), (4,-2), (5,5).
D) (0,4), (1,4), (2,4), (3,4)