If you are in primary school, you will almost choose two or three books and read them one by one. Of course, you will find that the books are all the same. . .

Middle school is moderately difficult.

The New Method of Mathematics Competition edited by Huang Dongpo ranges from the difficulty of senior high school entrance examination to the difficulty of competition.

A set of blue pamphlets issued by East China Normal University is also easy to sub-topic, but it doesn't feel difficult.

There are also some books published by Zhejiang University.

For more difficult books, there are a series of books published by Hunan Normal University Press, which can be used as appropriate.

You need more than one or two books to achieve something in high school.