Must see. The wrong problem set is a very useful study note. Moreover, you must find out the ins and outs of the wrong question. What matters is the way to solve the problem. Some topics are stem changes, and the ideas are the same. If you master the wrong questions, you won't waste the ones you have done. After all, I did the right question and will do it next time. If you don't correct the wrong questions and master the methods, you will make mistakes next time, so the questions you originally did are worthless. So I suggest that you must understand the wrong question. This is my learning experience, which is very useful. Hope to adopt