7Nunan D. Language Teaching Methodology: A Textbook for Teachers[M].Englewood cliffs,NJ: Prentice Hall Inc, 1991: 189.
8Krashen, S. The Input Hypothesis : Issues and Implications [M]. London : Longman, 1985 : 87-91.
9Swain M. Three functions of output in second language learning [M]. Oxford University Press, 1995 : 63.
10Long, M. H. & C. J. Sato. Classroom Foreigner Talk Discourse: Forms and Functions of teachers' Questions [ M ]//In H. Selinger & M. Long(eds.). Classroom Oriented Research in Second Language Acquisition.Rowley, Mass : Newbury House, 1983.