Which set of ordered pairs represents a function?
{(2, –2), (1, 5), (-2, 2), (1, –3), (8, –1)}

{(-3, –1), (-7, 1), (–6, –1), (-8, 1), (2, –1)}

{(1, 8), (5, 2), (2, –5), (1, –3), (–2, 9)}

{(–3, 1), (6, 3), (4, 2), (6, –3), (1, –1)}