Conrad, S., & Biber, D. (2001). Variation in English: Multi-dimensional studies. Longman.
Lua i Stíl Chicago (17ú heag.)Conrad, Susan, agus Douglas Biber. Variation in English: Multi-dimensional Studies. Harlow, Eng: Longman, 2001.
Lua MLA (9ú heag.)Conrad, Susan, agus Douglas Biber. Variation in English: Multi-dimensional Studies. Longman, 2001.
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