Which of the following relations describes a function?


A. { (0, 0), (0, 2), (2, 0), (2, 2) }
B. { (2, 2), (2, 3), (3, 2), (3, 3) }
C. { (2, -1), (2, 1), (3, -1), (3, 1) }
D. { (-2, -3), (-3, -2), (2, 3), (3, 2) }