5KRASHEN S. The input hypothesis: Issues and implica- tions [M]. New York: Longman, 1985.
6SWAIN M. Three functions of output in second language learning [ A ]. In C. Cook & B. Seidlhofer. Principles and Practice in Applied Linguistics [ M ]. Oxford: Oxford University Press. 1995 : 125 - 144.
7BROWN H D. Teaching by principles : An interactive ap- proach to language pedagogy [ M ]. Beijing: Foreign Lan- guage Teaching and Research Press, 2001 :84.
8WILLIS J A framework for task - based learning [ M ]. London : Longman, 1996.
9RAYMOND E B. Learners with mild disabilities: A char- acteristics approach (2nd ed. ). Needham Heights, MA : Allyn & Bacon, A Pearson Education Company, 2000: 176.
