AcknowledgementsFirst of all, I wish to express my warmest gratitude to my supervisor, Mr
Liao Yunquan, not only for his invaluable suggestions and comments on my thesis, but also for his rigorous attitude and great encouragement
I couldn’t have finished my whole thesis without his instructive suggestions and guidance
Next, I owned my thanks to my classmates and friends, who have offered me suggestions and several precious references which have proved to be quite useful in my thesis writing
Last but certainly not least, I am particularly thankful to my parents who encourage me and provide me a good environment
Without their encouragement and support, I would have been beaten down by difficulties
AbstractWith the advance of globalization, the communication between different countries has