Writing ideas: speak methodically and clearly. Arrange the materials in a reasonable order according to the time. There are three kinds of general narration: direct narration, flashback and interpolation. Be detailed and appropriate, and highlight the key points. The materials of general events are divided into primary and secondary, which can reflect the center of the article. This part should be written in detail, and the secondary content can be slightly written or not, which will leave a deep impression on readers.

This paper was completed under the careful guidance of my tutor, Researcher Wang Lan. From the topic selection of the paper, the solution of difficulties, to the typesetting of the article, all the efforts of the tutor are devoted to it. I was deeply impressed by Mr. Wang's rigorous academic attitude, profound knowledge, generous demeanor and extreme responsibility for students' study. Here, I would like to extend my high respect and heartfelt thanks to Mr. Wang!

I am very grateful to associate researchers Dai Xianchun and Wang Tong for their selfless help in completing my project.

Thanks again to all the teachers, classmates and friends who helped me with my graduate school. Thanks to my family. I will always miss this wonderful time.