6Vogostsky,L.S,trans.A.Kozulin.Thought and lan-guage〔M〕. . 1986
7Pica T,Kanagy R,Falodun J.Choosing and using communicative tasks for second language instruction. Tasks and Language Learning: Integrating Theory and Practice . 1993
8Rost M.Listening in language learning. . 1990
9Long,M.Task, group and task-group interaction. University of Hawaii Working papers in English as a Second Language . 1989