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