3Hatch, E. Psycholinguistics: a second language perspctive[M].Rowley Mass: ewbury House. 1983.
4Krashen, S. Et al. (eds.) Child - adult Difference in Second Language Acquisition[M]. Rowley Mass: Newbury House. 1982.
5Littlewood, W. Foreign and Second Language Learning [M].Cambddge University Press. 1984.
6Lenneberg, E. Biological Foundation of Language[M]. New York: Wiley.1967.
7David Crystal. The Cambridge Encyc-lopedia of Language[M].The Press Syndicate of the University of Cambridge. 1987.
8Stern, H. Issues in Early Core French: A selective and Preliminary Review of the Literature 1975-1981 [M]. Toronto: Board of Education. 1982.
9Johnson J., & Newport E. Critical Period Effects in Second Language Learning: the Influence of Maturational State on the acquisition of English as a Second Language[J]. Cognitive Psychology, 1989,21.
10Oyama S.The Sensitive Period and Comprehension of Speech[J]. Working Papers on Bilingualism, 1978.6.