Which set of ordered pairs represents a function?

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