Determine which relation is a function.
1: {(-5, 1), (-2, 0), (-2, 2), (3, 4), (6,2)}
2: {(-5, 3), (-2, 0), (-1, 2), (6, 4), (6, 3)}
3: {(-5, 1), (-5, 0), (-2, 1), (-1, 4), (6, 2)}
4: {(-5, 1), (-2, 0), (-1, 1), (2, 4), (6, 3)}