All books are based on textbooks. It's too early to do it now. Let's do it in senior three. Wang Houxiong's topic is really difficult. Buy a book that suits you. What others think is good does not necessarily mean that it is used well. See what the teacher recommended. In short, buying reference books should be based on personal needs. Moreover, in fact, self-study is a bit bad, that is, I think I will. If I don't listen to the teacher carefully in class, the effect will be very poor. If my personal ability is relatively high, I don't have any good suggestions for self-study or anything.