7Appel, C. and Mullen, T. Pedagogical considerations for a web- based tandem language learning environment [ J ].Computers and Education,2000,34 ( 3 - 4) :291 - 308.
8Breen, M. Learner contributions to task design [ M ]. In C.Candlin and D. Murphy (Eds.) Language learning tasks.Englewood Cliffs NJ: Prentice - Hall, 1987.
9Littlewood, W. Communicative Language Teaching: An introduction[ M]. Cambridge: Cambridge University Press,1981.
10Nunan, D. Designing tasks for the communicative classroom[ M ]. Cambridge : Cambridge University Press, 1989.
