6Brown H D. Principles of Language Learning and Teaching[M]. London: Pearson Hall Regents, 1994.165.
7Johnson Keith. An Introduction to Foreign Language Learning and Teaching[M]. London: Pearson Education Limited, 2001.301-305.
8Krashen S. The Input Hypothesis: Issues and Implications [M]. London: Longman, 1985.39.
9Long M. Input and Second Language Acquisition Theory[A]. S Gass, C Madden . Input and Second Language Acquisition [C]. Rowley, Mass: Newbury House, 1985.16.
