There are several principles for reference: 1. Exercise quality: Exercises must cover core concepts, have a reasonable difficulty level, and preferably come wit

There are several principles for reference: 1. Exercise quality: Exercises must cover core concepts, have a reasonable difficulty level, and preferably come with answers or explanations. 2. Practice orientation: Deepen theoretical understanding and cultivate application capabilities by solving problems. 3. Classics and reputation: Give priority to books that have been recognized by the academic community or learners for a long time.