Which is a function?
O {(-3,5), (1,4), (3,7), (1,7),(4,9)}
O {(7,9), (13,-2), (8,4), (7,0), (4,12)}
O {(2,1),(-1,7), (6,-2), (10,3), (-6,0)}
O {(-2,4), (7,4), (-6,8), (-2,8), (1,1)