万方数据 Contents Abstract ................................................................................................................................................................... i 摘要.................................................................................................................................................................... iii List of Abbreviations ............................................................................................................................................. v List of Tables ......................................................................................................................................................... vi Chapter1 Introduction .......................................................................................................................................... 1 Background of the Research ...................................................................................................................... 1 Purpose and Significance of the Study ...................................................................................................... 2 Layout of the Paper ................................................................................................................................... 3 Chapter 2 Literature Review ................................................................................................................................ 5 .....................................................................