Which relation is not a function? 1) {(1, 5), (2, 6), (3, 6), (4, 7)}
2) {(4, 7), (2, 1), (−3, 6), (3, 4)}
3) {(−1, 6), (1, 3), (2, 5), (1, 7)}
4) {(−1, 2), (0, 5), (5, 0), (2, −1)}