Which relation is a function?


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


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


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


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