A book about postgraduate mathematics.
To tell the truth, I don't remember much after reading a book for the first time, but I suggest you finish reading the book first, don't do the questions, just read the general concept and get to know it, and then you can buy a review book. Li Yongle's books are still very good, because many books can't pass the exam, so you should first understand the exam outline, and then read only a few books in a targeted way. When reading a review book, you can look at the topic and the first one.