Acknowledge First and foremost， I appreciate my college which gives me a comfortable learning Second， I would like to show my deepest gratitude to my supervisor， Miss Zhang， who has walked me through all the stages of the writing of this Without her illuminating instruction and patience， this thesis could not have reached its present I am also greatly indebted to all my teachers who have helped me to develop the fundamental and essential academic My sincere appreciation also goes to all my classmates， who are my proud of my Last but not least， I want to thank all my friends， especially my three lovely roommates， for their encouragement and
