Guffey, M. E. (2010). Essentials of business communication 2nd ed. Cengage Learning.
Lua i Stíl Chicago (17ú heag.)Guffey, Mary Ellen. Essentials of Business Communication 2nd Ed. Cengage Learning, 2010.
Lua MLA (8ú heag.)Guffey, Mary Ellen. Essentials of Business Communication 2nd Ed. Cengage Learning, 2010.
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