Yorkey, R. C. (1977). English for international communication. Jilid 2. American Book.
Lua i Stíl Chicago (17ú heag.)Yorkey, Richard C. English for International Communication. Jilid 2. American Book, 1977.
Lua MLA (8ú heag.)Yorkey, Richard C. English for International Communication. Jilid 2. American Book, 1977.
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