First of all, I am very grateful to my tutor, Professor xxx. His useful suggestions, incisive comments and constructive criticism have made great contributions to the completion of this paper. She spent quite a lot of time reading my manuscript and put forward suggestions for further revision. I can't express my great help to her in words. She helped me establish an analytical framework and reviewed the draft of this paper many times. Her careful care in life also deserves my thanks.

I am also very grateful to all the teachers who have helped me directly or indirectly in my study. Any progress I have made is the result of their deep concern and selfless dedication. Among them: Professor xxx.

Finally, I would like to thank my friends, who spent a lot of time and energy expressing their opinions on the draft.

Without their patient help and friendly encouragement, I couldn't have finished this paper in such a short time without lowering its academic quality. Thank you very much for giving me time so generously. Indeed, without their hard work, it is impossible to revise and improve my draft and complete the current paper.

Thank you very much