If A and B are two sets such that every element of A is in B and every element of B is in A, then
AA and B are necessarily disjoint
BA is a proper subset of B but A ≠ B
CA is a superset of B but A ≠ B
DA is equal to B (A = B)
Answer & Solution
Correct answer: D. A is equal to B (A = B)
Bidirectional inclusion (A ⊆ B and B ⊆ A) is the definition of set equality. Proper subset rules out equality, so options A and B are wrong; disjointness contradicts the inclusion.
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