Acknowledgments My deepest gratitude goes first and foremost to Professor Lu Chunmei, my supervisor, for her constant encouragement and guidance
She has walked me through all the stages of the writing of this thesis, given me suggestions on the topic and encourage me to finish the thesis
Without her consistent and illuminating instruction, this thesis could not finish successfully
Second, I extend my thanks to Professor Li Qiang and every teacher who has helped me with useful suggestions on the structure in his class
Besides, my thanks would go to my beloved family for their loving considerations and great confidence in me all through these years
I also owe my sincere gratitude to my friends and my fellow classmates who gave me their help, encourage and time in listening to me and hel