Which relation describes a function?

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