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- Image: Dictionariesby Newton Free Library under CC BY-NC-ND 2.0
- Image: Students in Classroom by Longrihui under CC BY-NC-ND 2.0
- Image: Students at Table by Elatb under CC BY-SA 3.0
- Duppenthaler, P. "Vocabulary Acquisition: the Research and its Pedagogical Implications"
- Image: Teacher Teaching by Frank Klaus Schneider under CC BY-NC-ND 2.0