Warshawsky, D. (1994). Spectrum 4: A communicative course in English. Workbook. Prentice Hall Regents.
Chicago-referens (17:e uppl.)Warshawsky, Diane. Spectrum 4: A Communicative Course in English. Workbook. London: Prentice Hall Regents, 1994.
MLA-referens (9:e uppl.)Warshawsky, Diane. Spectrum 4: A Communicative Course in English. Workbook. Prentice Hall Regents, 1994.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.