Determine which relation is a function.

a.
{(–4, 3), (–2, 3), (–1, 2), (2, 5), (3, 2)}

b.
{(–4, 1), (–2, 3), (–2, 1), (–1, 5), (3, 2)}

c.
{(–4, 1), (–2, 3), (–1, 2), (3, 5), (3, 2)}

d.
{(–4, 1), (–2, 3), (–1, 1), (–1, 5), (3, 2)}