5Krashen, S. 1985.The Input Hypothesis: Issues and Implications[M].London: Longman.
6Long,M.H.and C.J.Sato.1983.Classroom Foreigner Talk Discourse: Forms and Functions of Teachers' Questions [C ]//H.W.Sliger & Long,M.H. (eds.) Classroom Oriented Research in Second Language Acquisition.Rowley, Mass: Newbury House.
7Swain, M. 1985:Communicative competence: Some roles of comprehensible input and comprehensible output in its development [C]//S. Gass & C. Mad- den (Eds.). Input in Second Language Acquisition. Rowley, Mass: Newbury House, 248-249.