Which of the following sets of ordered pairs represents a function?

{(−3, −3), (−2, −2), (−1, −1), (0, 0), (1, 1)}
{(−3, −3), (−3, −2), (−3, −1), (−3, 0), (−4, −1)}
{(−3, −3), (−3, −1), (−1, −2), (−1, −1), (−1, 0)}
{(−3 −3), (−3, 0), (−1, −3), (0, −3), (−1, −1)}