Sheeler, W. D. (1991). WELCOME TO ENGLISH BOOK 4. English Language Service.
Lua i Stíl Chicago (17ú heag.)Sheeler, Willard D. WELCOME TO ENGLISH BOOK 4. English Language Service, 1991.
Lua MLA (8ú heag.)Sheeler, Willard D. WELCOME TO ENGLISH BOOK 4. English Language Service, 1991.
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