6Brown, H. D. 1994. Principles of Language Learning and Teaching[M]. Beijing: For- eigu Language Teaching and Research Press.
7Odlin, T. 1989. Language Transfer [M]. Cam- bridge:Cambridge University Press.
8Richards, J. C. etc. 2005. Longman Dictio- nary of Language Teaching and Applied Linguistics [M]. Beijing: Foreign Language Teaching and Research Press.