Q. Which relation is a function?

1. {(4, 0), (4, 1), (4, 2), (4, 3)}
2. {(–1, 3), (–2, 6), (0, 0), (–2, –2)}
3. {(7, 4), (8, 8), (10, 8), (10, 10)}
4. {(–2, –2), (0, 0), (1, 1), (2, 2)}