1Hu,Zhuanglin.(1988)Linguistics.A Course Book.Beijing:Bei-jing University Press.Krashen,S.(1981).Second Language Ac-quisition and Second Language Learning[M].Oxford:Penguin.
2Widdowson,H.G.Teaching Language as Communication.(1989):Oxford University Press.
3Littlewood,W.Communicative Language Teaching.Beijing:For-eign LanguageTeaching and Research Press,2000.