According to the meaning of the question, B belongs to A, that is to say, B is an element in set A, so what may happen to B is 1, 2,3, or an empty set?

Question 2: Ownership is not equal to, but contains. For example, the set A {1, 2,3}, where 1 belongs to a, 2 belongs to a, and 3 belongs to a, but 1 does not equal {1, 2,3}, and 2 does not equal {1, 2,3}.