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)}