Answer: Third option.
Explanation:
A ⊂ B this means that A is subset of B.
If A is subset of B (A ⊂ B), then all the elements of A belong to the subset B.
For example, the set of the Natural numbers is a subset of the Real Numbers.
Then, A ∩ B are all the elements that belong to AB at the same time.
A ∪ B are all the elements of A and all the elements of B.
But if we already said that A is inside of B, then:
A ∩ B = A ≠ A ∪ B
A ∩ B = A ∪ B only happen when the set A=set B.
Therefore, the answer is: NEVER.