Duncan, D. J. (1979). Programmed learning aid for retailing: Modern concepts and ractices. Learning System.
Chicago-viite (17. p.)Duncan, Delbert J. Programmed Learning Aid for Retailing: Modern Concepts and Ractices. Homewood, III.: Learning System, 1979.
MLA-viite (9. p.)Duncan, Delbert J. Programmed Learning Aid for Retailing: Modern Concepts and Ractices. Learning System, 1979.
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