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