... I would like to express my deep gratitude to all my teachers at College of Foreign Languages, Vietnam National University-Hanoi for their valuable lectures. And their knowledge, their thoughtfulness ... knowledge, their thoughtfulness as well as their sympathy I will always appreciate.For the accomplishment of this study, I wish to show my sincere thanks to my supervisor Mr. Nguyễn Bàng, who has ... helped me during the period of my study at College of Foreign Languages, VNU-Hanoi.Finally, I wish to thank my wife for the love she gives me and her encouragement in my doing this thesis. ...