Which set of ordered pairs represents a function?
{(-7,-1), (7,-1),(-9,3), (-9,2)}
{(3,5), (7,9),(4,4), (3,3)}
{(3,-2), (-7,6),(-5, -8), (3, -6)}
{(0,2).(-9,7),(-6, -1),(-2,2)}