The sets of ordered pairs below represent relations.

1. (0,0), (1,1), (2,2), (3,3), (4,4)
2. (1,2), (2,1), (1,3), (0,1), (3,1)
3. (0,2), (1,2), (2,4), (3,4), (3,6)
4. (1,6,), (2,6), (3,6), (4,6), (5,6)

Which of these sets are also functions?

1 only
1 and 4
2 and 3
2,3, and 4