Which set of points represents a function?
A. {(1,3), (1,-5), (2, 4), (2,5)}
B. {(4, -2), (4,0), (4, 1), (4, 2)}
C. {(2, 1), (7, 9), (3, 12), (4, 10)}
D. {(2, 4), (-2, 3), (2, 5), (-2, 1)}