8Ure,Jean.Lexical Density and Register Differentiation[A]. In Perren,G.E.& Trim,J.L.(eds.).Application of Linguistic:Selected Papers of the 2nd International Conference of Applied Linguistics[C].Cambridge: Cambridge University Press,1971:443-452.
9Nation,I.S.P.Teaching and Learning Vocabulary[M]. Newbury House Publishers,1990.
10Nation,I.S.P.Second Language Vocabulary.In K.Brown (Ed.)Encyclopedia of Language and Linguistics(2nd ed.)[M]Oxford:Elsevier,2006:48-454.
