Correct me if I am wrong:
A: B might not use some values of C. But B cannot have anything that C doesn't contain. So the difference will be phi. This is the Ans.
B: Same as option A, C might have values that B doesn't use so the diffenerce cannot be phi here. Moreover the Q askes which one is always true, this one might not be true in some cases.
C: Same argument, B and C might not be equal always.
D: Difference is phi, proven in option A.