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