Which relation is a function?
{(5, –4), (–4, 5), (–5, 4), (4, –5)}
{(8, –5), (–5, 8), (–5, –8), (–8, 5)}
{(–7, 6), (6, –7), (–7, 9), (10, 3)}
{(2, –3), (–3, 2), (2, 3), (–2, 3)}
{(5, –4), (–4, 5), (–5, 4), (4, –5)}
{(8, –5), (–5, 8), (–5, –8), (–8, 5)}
{(–7, 6), (6, –7), (–7, 9), (10, 3)}
{(2, –3), (–3, 2), (2, 3), (–2, 3)}