5. Which of the following is a function?
A. (1,7), (2,14), (3, 21), (1, 28)
B. (0, A), (5, B), (10, C), (15, D), (5, E)
C. (-5,1),(-10,1),(-15, 1), (-20,1),(-15,1)
D. (1, 1), (2, 2), (3, 3), (4,4), (5,5)