All the content here is compiled and copied from the Internet. It is not original and has some shortcomings. If there are any mistakes, you are welcome to correct them. If necessary, you can copy and download them, but we reject any nonsense for any reason.
PS: 1. Because it is copied from the Internet, if there is any infringing content, it is not intentional. As long as someone points it out, Mulan will immediately delete the relevant content.
2. Some of the theoretical knowledge involved here will appear in Mulan's new article.
3. This article refuses to be dragged out into the clear water in any form.
Intention: