4Gass, M.S.&Schachter, J. Lingustic Perspectives on Second Language Acquisition [ M] .New York: Cambridge Univer-sity Press, 2006.
5Swain, M. Canmunicative Competence. Gass, S.&Madden. Some Roles of Comprehensive Input and Comprehensive Output in its Development [A] . Newbury House, 1985.
6Lightbown, P. Exploring Relationships Between Develo- pmental and Instructional Sequences in L2 Acquisition. In H.W. Seliger and M. H. Long (eds.), Classroom-oriented Research in Second Language Acquisition. Rowley, Mass.: Newbury House, 1983.
7Chomsky N.Knowledge of Language: Its Nature, Origin and Use[]..1986
8Krashen,S. D.Lateralization, language learning and the critical period: some new evidence[].Language Learning Journal.1973
9Terzaghi K,Peck R B.Soil mechanics in engineering practice[]..1967
