Which set of ordered pairs does not represent a function?
{(0,9),(-1,-2), (-5,2), (-3,0)}
{(0, -6),(-6,5), (4,5), (5,7)}
{(0,8),(-7, -1), (4,8), (1,5)}
{(4, -6), (9, – 7), (9,-4), (6,3)}