Which set of ordered pairs represents a function?

{(2, –2), (1, 5), (–2, 2), (1, –3), (8, –1)}
{(3, –1), (7, 1), (–6, –1), (9, 1), (2, –1)}
{(6, 8), (5, 2), (–2, –5), (1, –3), (–2, 9)}
{(–3, 1), (6, 3), (–3, 2), (–3, –3), (1, –1)}

A set of ordered pairs is a function as long as no two ordered pairs have the same first coordinate with different second coordinates.

{(2, –2), (1, 5), (–2, 2), (1, –3), (8, –1)}

It is not a function by above definition(since, 1 have 2 images)

{(3, –1), (7, 1), (–6, –1), (9, 1), (2, –1)}

It is a function  

{(6, 8), (5, 2), (–2, –5), (1, –3), (–2, 9)}

It is not a function(since, -2 have more than 1 image)

{(–3, 1), (6, 3), (–3, 2), (–3, –3), (1, –1)}

It is not a function (since, -3 have more than 1 images)