1. Bai, Quan. 2000. Misconceptions in the teaching and learning of bu and mei (you). Language Teaching and Learning (3): 21–25. (In Chinese)
2. Biber, Douglas, Stig Johansson, Geoffrey Leech, Susan Conrad, & Edward Finegan. 1999. Longman grammar of spoken and written English. London: Longman.
3. Chafe, Wallace L. 1995. The realis-irrealis distinction in Caddo, the Northern Iroquoian languages, and English. In Modality in grammar and discourse, eds. Joan Bybee, and Suzanne Fleischman, 349–365. Amsterdam: John Benjamins.
4. Chang, Suk-Jin. 1996. Korean. Amsterdam: John Benjamins.
5. Chao, Wynn. 1994. Negation as adverb in Chinese. In SOAS working papers in linguistics and phonetics (Vol. 4), 232–242. London: University of London.