3Krashen, S. 1985. The Input Hypothesis: Issues and Implications [M]. London: Longman.
4Laufer, B. 1998. The development of passive and ac- tive vocabulary in a second language: same or dif- ferent? [J]. Applied Linguistics, 19 (2): 255-271.
5Lewis, M. 1993. The Lexical Approach [M]. Hove: Language Teaching Publications.
6Nation, I. 1990. Teaching and Learning Vocabulary [M]. Boston: Heinle & Heinle Publisher.
7O'Malley, J. M. & Chamot, A. U. 1990. Learning Strategies in Second Language Acquisition [M]. Cambridge: Cambridge University Press.
