First of all, I would like to express my sincere and special gratitude to Mrs.
Pham Thi Bich Ngoc, my supervisor, who has generously given me invaluable
assistance and guidance during the preparation of this graduation paper. The
success of my paper would be almost impossible without her tireless support.
Secondly, I would be grateful to Mrs. Dang Thi Van, my second supervisor, for
her precious advice and encouragement.
Furthermore, I own a particular debt of gratitude to Mrs. Tran Ngoc Lien, Dean
of Foreign Language Department of Hai Phong Private University for her
supportive lectures and references.
In addition, my thanks also go to other teachers of Hai Phong Private University
for their great contribution as well as their lecture.