Which set of ordered pairs represents a function?

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