2Birdstone D, Second Language Acquisition and the Critical Period Hypothesis [ M ]. London: Lawrence Erlbaum Associates, Publishers, 1999,
3Ellis R. The Study of Second Language Acquisition[ M ]. Oxford: OUP. Rpt. by Shanghai: Shang-hai Foreign Language Education Press, 1999.
4Larsen-Freeman, Diane, and Michael H Long. An Introduction to Second language Acquisition Research[M]. london: Longman. Rpt. by Beijing: Foreign Language Teaching and Research Press, 2000.
5Richartis Jack C et al (ed.) Longman Dictionary of Language Teaching and Applied Linguistics.[Z] (English-Chinese Edition). london: Longman. Rpt. by Beijing: Foreign Language Teaching and Research Press, 2000.