Acknowledgments
First of all, I am deeply appreciate to my tutor Ms. Chen. She gave me lots of valuable information and instructions and helped me to complete my every step of finishing the final thesis. I am mostly grateful to her guidance and patience.
I also would like to thank others teachers who have taught me in the past four years with great patience. I really benefited from that.
Moreover, I like to thank all my friends who helped me in writing this thesis in searching for information and bibliography.
Last, I sincerely would like to dedicate the thesis to my parents and Wang Jing who have been supporting me in my study life.
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