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) $(R \cup S) = S$
b) $(R \cap S) = (S \cap R)$
c) $((R - S) \cup (S - R)) \cap (R \cap S) = \emptyset$
d) $(R - R) = (S - S)$