Which of the following sets of ordered pairs is not a function?
{(0, 2), (1, 4), (2,5), (3, 6)}
{(-1, 2), (1, 3), (1,5), (-3, 4)]
{(0, 2), (1, 2), (2, 2), (3, 2)}
{(-4,3), (-1, 1), (-2,5), (3, 7)}