Determine which relation is a function.

A. {(–5, 1), (–5, 0), (–2, 1), (–1, 4), (6, 2)}

B. {(–5, 1), (–2, 0), (–2, 2), (3, 4), (6, 2)}

C. {(–5, 1), (–2, 0), (–1, 1), (2, 4), (6, 3)}

D. {(–5, 3), (–2, 0), (–1, 2), (6, 4), (6, 3)}

Please explain.