Acknowledgments

This book is based on my doctoral thesis,which was completed at the University of Auckland,New Zealand.I would like to express my sincere gratitude and appreciation to the many people who have helped me in the completion of my thesis.

I am grateful to my supervisor,Dr.Michael Barlow,for his assistance from the initial design of the research to the final refinement of the thesis.His detailed feedback helped me enormously in writing academically.He had devoted a huge amount of time reading my drafts.Having an attentive reader made me more careful and motivated in writing.I also benefited a lot from his expertise in statistics and corpus analysis method.His wisdom,compassion and support have made the task of writing less formidable,but even enjoyable to some extent.Even after graduation,Michael helped me revise the thesis for publication.I am greatly indebted to him.

I thank my co-supervisor,Dr.Helen Basturkmen,for her constructive and insightful comments,warm encouragement and great efficiency.Her feedback at various stages of my research made me ponder hard and gave the thesis more depth.

I extend my gratitude to Dr.Shaofeng Li for his assistance in statistics and Dr.Fred Kroon,Professor of Philosophy,who brought my attention to the relation between epistemology and academic writing conventions.

In addition,I would also like to thank the staff and my fellow PhD students in the Department of Applied Language Studies and Linguistics for their support,constructive criticism,and suggestions.

Finally,thanks must go to my family for their love,encouragement and assistance.