Which of the following relations is a function? A. (1, 0), (-2, 3), (9, 1), (-2, 5) B. (1, 4), (-2, 2), (9, 1), (-7, 2) C. (9, 1), (-2, 4), (1, 1), (9, 2) D. (1, 4), (-2, 6), (1, 3), (-7, 2)