It is necessary to brush some questions, but before brushing the questions, you should master the basic knowledge of the textbook in detail. If you encounter mistakes in brushing questions, you should go back to the textbook immediately and check whether your foundation is solid. At that time, the author thought that the textbook exercise was wrong, and he always believed it and revised the answer. It was not until recently that I found that answering others was right and embarrassing. At the same time, the current context has answered the doubts of the original study, so I think the foundation must be laid firmly, and then laid firmly.