Answer:
A-B
Step-by-step explanation:
It doesn't say A=B... But just that A is a subset of B.
Anyways, why not try an example to help reveal the answer.
Let the universe set, U, be U={1,2,3,4,5,6}.
Let B={1,2,3,4} and A={1,3,5}
First choice would become A'={2,4,6}
Second choice would become B'={5,6}
Third choice would become A-B={5}
Fourth choice is just { }
B'-A'={5}
The only choice matching is A-B
*Just so you know X-Y is the set of elements contained in X only if they are not also in Y.
