I am a graduate student, and I have also used Li Yongle's books. His classic 400 questions are difficult, but difficult to do. But every difficulty is reflected in the most basic level, and the superposition of multiple levels leads to a certain depth of this topic. But I think from the perspective of postgraduate entrance examination, this book is not suitable, slightly biased and slightly more difficult. If you can find a complete Li Yongle's book and take the postgraduate entrance examination directly, it will be almost complete. Of course, if you want to further improve yourself, you can try to do 400 questions in your spare time. The above is my personal opinion, I hope it will help you, and I wish you success in the postgraduate entrance examination.