Question

Which set is a function?
A {(2,6), (3,6), (4,6), (2,0)}{(2,6), (3,6), (4,6), (2,0)}
B {(0,3), (3,0), (0,4), (4,0)}{(0,3), (3,0), (0,4), (4,0)}
C {(6,2), (2,0), (4,6), (6,4)}{(6,2), (2,0), (4,6), (6,4)}
D {(0,4), (0,9), (12,6), (-3,9)}{(0,4), (0,9), (12,6), (-3,9)}
E {(0,2), (2,0), (4,6), (6,4)}