which relation is NOT a function?

Question

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)}

Answer 1

3) has two values of y for x = 1
three and negative seven

Answer 2

thank you