Which set of ordered pairs represents a function?

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