感谢研究中心的同学们，我们在学业上共同进步，生活上互相关心，度过了很多美好、快乐的时光。感谢他们在学习上、生活上给予我的关怀和帮助;同时也营造了轻松的学习环境，促使着我努力学习，共同进步。
感谢管理学院两年来对我的培养，感谢学院各级领导、老师对我的大力支持和帮助，在此深表谢意!
衷心感谢我的家人，是他们一直默默地在支持着我，鼓励着我，是我学习进步的坚强后盾，在我困惑、迷茫的时候为我指明了前进的方向，让我找回了学习、生活的自信。
最后，感谢所有关心、帮助过我的人。
i would like to extend my deep gratitude to all those who have offered me a lot ofhelp and support in the process of my thesis writing.
first and foremost, my sincere thanks go to professor li changbao, my supervisor,who has offered me numerous valuable comments and suggestions with incomparablepatience and encouraged me profoundly throughout my postgraduate study. without hispainstaking teaching and insightful advice, the completion of this thesis would havebeen impossible.
also, i owe many thanks to all the professors who have taught me during myprevious study in this university, for leading me into a challenging yet fascinating fieldof academic research. the profit that i gained from them will be of everlastingsignificance to my future research.
last but not least, i am deeply indebted to my family and friends, who have helpedme and shared with me my worries, frustrations, and happiness.
