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