Which of the relations below is a function? * 2 points

{(2, 3), (3, 4), (5, 1), (2, 4)}

{(2, 3), (3, 4), (6, 2), (7, 3)}

{(2, 3), ( 3, 4), (6, 2), (3, 3)}

{(2, 4), ( 3, 4), (6, 3), (3, 3)}