1Yule, G. The Study of Language [M]. Beijing: Beijing Foreign Language Teaching and Research Press and Cambridge University Press, 2006. 1-2.
2Aitchison, J. The Seeds of Speech: Language Origin and Evolution [M]. Beijing: Beijing Foreign Language Teaching and Research Press and Cambridge University Press, 2002.
3Aronoff, M & Janie, R. The Handbook of Linguistics [M]. Beijing: Beijing Foreign Language Teaching and Research Press and Cambridge University Press, 2001.