9Biber, D., E. Finegan, S. Johasson, S. Conrad&G. Leech. 1999. Longman Grammar of Spoken and Written English [M]. Beijing: Foreign Language Teaching and Research Press.
10Biber, D. & F. Barbieri 2007. Lexical bundles in university spoken and written registers [J]. English for Special Purposes 26: 263-286.