7LIGHTBOWN P M,SPANDA N.How language are learned. . 1999
8MACKEY W F.The importation of bilingual education models. Georgetown University roundtable:International dimensions of education . 1978
9ASHER J J,GARCiA R.The optimal age to learn a foreign language. The Modem Language Journal . 1969
10JOHNSON J S,NEWPORT E L.Critical period effects on universal properties of language:The status of subjacency in the acquisition of a second language. Cognition . 1991