Which relation is a function?

Responses

{(1, 2), (2, 3), (3, 4), (4, 5)}


{(1, 2), (3, 4), (5, 6), (1, 8)}​

{(1, 2), (2, 1), (1, 3), (3, 1)}


{(0, 2), (0, 4), (0, 6), (0, 8)}