6Krashen, S. D. The Input Hypothesis: Issues And Implications[M]. Longman Group Limited,1985.
7Swain, M. Three functions of output in second language learning [A]. In Cook. G. & Seidlhofer, B.(eds.) Principles & Practice in Applied Linguistics [M]. Oxford University Press,1995.
8Swain,M. Problems in Output and the Cognitive Progresses They Generate: A Step Towards Second Language Learning [J]. Applied Linguistics,1995,16 (3).
9Gay, L. R. Educational Research-Competencies For Analysis And Application[M]. (5thed.) Prentice-Hall,Inc, 1996.
