Which of the relations below is a function?


A. {(2,3), (3,4), (5,1), (6,2), (2,4)}

B. {(2,3), (3,4), (5,1), (6,2), (7,3)}

C. {(2,3), (3,4), (5,1), (6,2), (3,3)}

D. {(2,3), (3,4), (5,1),(6,1), (6,3)}