4Krashen S. The Input Hypothesis: Issues and Amplications[M]. London:Longman, 1985.
5SwainM. Communicative Competence: some roles of comprehensible input and comprehensible output in its development [A]. S. Gass, C. Madden. Input in Second Language Acquisition [C]. Rowley, MA: NewburyHouse Pubishers. 1985.