Which set of ordered pairs represents a function?

A (1,8). (8, 1), (1,5), (5, 1)
B (2, 1), (3, 1). (4.3). (5,3)
С (5, 1), (3, 3), (3, 7), (7, 1)
D (5, 1), (5,6), (1,3), (9,7)

Q&A Education