help me
1. Circle each relation that is a function.
{(1, 3), (1, 5), (2, 7), (3, 9), (4, 11)}
{(0, 0), ( 21, 21), ( 22, 22), ( 23, 23)}
{(5, 5), (5, 4), (5, 3), (5, 2)}
{(2, 5), (3, 5), (4, 5), (5, 5)}