Which of the following relations is a function?

A(7, 1), (-2, 4), (2, 1), (7, 2)

B(2, 4), (-2, 2), (7, 1), (-6, 2)

C(2, 0), (-2, 3), (7, 1), (-2, 5)

D(2, 4), (-2, 6), (2, 3), (-6, 2)