In the process of writing this paper, I would like to thank my instructor for his guidance and supervision. Without the help of the teacher, there would be no today's paper. The course of study is hard, but also happy. In this process, Mr. Liang is always strict with me, without any carelessness. In view of some of my problems, he is always able to put forward targeted opinions. At the same time, he pays more attention to the cultivation of my self-study ability.