If a ⊂ b, then a ∩ b = a ∪ b.

always
sometimes
never

Third option.

Step-by-step 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.

step-by-step explanation:

this is not a question