Which relation is a function?



{(6, 0), (–7, 14), (–2, –5), (–2, 5)}



{(–1, 3), (5, 3), (–6, 7), (9, 0)}



{(0, –7), (4, –8), (0, –9), (4, –10)}



{(2, 4), (2, –7), (2, 11), (2, –15)}