Problems related to attributive clauses in English

Solution: First of all, the leading word at the beginning of the sentence leads to the subject clause, so you can't use which, you can only use what or all that.

Answer some questions, please wait a moment.

When what leads the subject clause, what acts as a predicate in the sentence, but the sentence lacks the object of thinking, so it is appropriate;

When which leads the subject clause, which generally acts as an attribute and modifies nouns, such as which one. However, there is no thinking object in this sentence, so it can't be used alone.

And what=all is equivalent to that leading attributive clause modifying all, so there is no suitable answer to this question ~