5. Let R(A,B,C) and S(A,B,C) be two relations. Which of the following is true if R, S, and all operations are interpreted to be sets and set-operations, but not necessarily true if R S and all operations are bags and bag-operations? a) (R [union] S) = S b) (ROS) = (SNR) O c) (((R-S) [union] (S - R)) N (ROS)) = [emptyset] d) (R-R) = (5 - S)