Most of the questions are within the thinking range of the senior high school entrance examination, and everyone's thinking about doing the questions is very high. Tsinghua High School uses books every year.

High-level categories: Olympic Mathematics courses, intensive lectures and tests on Olympic Mathematics, etc.

I especially recommend this year's "Lecture and Test of Olympic Mathematics Intensive Reading". Starting to make this set of books at low cost has made me find many bright spots!

Finally, I recommend a book, The Last Question of the Challenge.