Which set of ordered pairs represents y as a function of X?
A {(1,5), (3, 1), (2,7), (1,8)}
B {(8,2), (4,3), (7,2), (8, 6)}
C {(6,3), (3, 5), (2,5), (9,6)}
D {(4,7), (4, 6), (4,4), (4,1)}