2. English
[1] Andrea B. Geffner. How to Write Better Business Letters. 3rd Edition, New York: Barrons Educational Series, 2000
[2] Crystal, David. Language and The Internet. Cambridge University Press, 2001
[3] Frailey, L. E. Handbook of Business Letters, Third Edition, Prentice Hall, 1989
[4] Leech, G. N. Principles of Pragmatics. New York, Longman, 1983