(i) ⇔ (ii):
A⊂B ⇔ All elements of A are in B ⇔ A – B = φ
(ii) ⇔ (iii):
A-B = φ⇔ All elements of A are in B ⇔ A∪B = B
(iii) ⇔(iv)
A∪B = B ⇔ All elements of A are in B ⇔ All elements of A are common in A and B.
⇔ A∩B = A
∴ All the four given conditions are equivalent.