If A⊂BA \subset BA⊂B, then which of the following is always true?
B∖A=∅B \setminus A = \emptysetB∖A=∅
A∩B=BA \cap B = BA∩B=B
A∖B=∅A \setminus B = \emptysetA∖B=∅
A∪B=AA \cup B = AA∪B=A