6[3]S. C. Levinson. Pragmatics [M]. Cambridge: Cambridge University Press,1983.
7[2]Levinson S C (1983) Pragmatics,Cambridge:Cambridge University Press.
8Hyland, K. Hedging in academic writing and EAP textbooks [ J ].English for Specific Purposes, 1994, 13(3): 239- 255.
9Hyland, K. Writing without conviction? Hedging in science research articles [J]. Applied Linguistics, 1996,17(4): 433 - 454.
10Kuo, Chin-hua, The use of personal pronouns: Role Relationship in scientific jonrnal articles [J]. English for Specific Purposes, 1999, 18(2):121 - 138.
