Which set of ordered pairs does not represent a function?

{(-4,3), (1,-6),(-8,-1), (1,9)}
{(9,-8),(-8,-5), (3,-8),(-1,-6)}
{(2,4),(-3,-8),(-4,-8), (1, -7)}
{(-9,5), (9,0), (2,5), (-1,-6)}