In particular, the 2 of 1 and 1 are contradictory.

1 empty set ∈ {empty set} can be understood as this empty set is not? . Empty set as an element or directly considered as an ordinary word. Explain it this way. I wonder if you can understand.

2 empty set? {empty set} This empty set is a set. I don't know whether you wrote the teacher's narrative or the teacher wrote it on the blackboard. I think it should be {empty set}

Then 3 should be understandable.

If you agree with my understanding above, you can understand 1 of seconds.

2, ? This is a collection. So {1, 2,3} can't be written as {? , 1,2,3}。

If you really meet {? , 1,2,3}。 Here? This can be seen as a symbol and an element.

Well, there's really no need to be too entangled. . . It is enough to solve the problem in the macro direction. The college entrance examination should not have such painful questions. Hmm. How interesting