2Krashen S. Principles and Practice in Second Language Acquisition [ M]. Oxford: Pregamon, 1982.
3Krashen S. The Input Hypothesis: Issues and Implication [ M]. London: Longman, 1985.
4Swain, M. Communicative competence: Some roles of comprehensible input and comprehensible output in its development [A]. In S. Gass & C. Madden (eds.) Input in Second Language Acquisition. Rowley [C]. MA: Newbury House, 1985.
5Swain. The Output Hypothesis: Just Speaking and Writing Arent Enough [ J]. The Canadian Modem Language Review, 1993.
6Marion Williams & Robert I.. Burden. Psychology for Language Teachers [ M ]. Cambridge: Cambridge University Press, 1997.
