Which of the following is not a function?

1. {(0,0), (1,4), (2,8) }
2. {(0,0), (3,16), (16,49) }
3. {(1,1), (2,2), (3,3), (4,4)}
4. {(7,1),(6,2), (5,3), (5,4)}
5. all of the choices are function