Tough, A. M. (1979). The adult's learning projects: A fresh approach to theory and practice in adult learning (2d ed.). Learning Concepts.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रTough, Allen M. The Adult's Learning Projects: A Fresh Approach to Theory and Practice in Adult Learning. 2d ed. Austin, Tex.: Learning Concepts, 1979.
एमएलए (8वां संस्करण) प्रशस्ति पत्रTough, Allen M. The Adult's Learning Projects: A Fresh Approach to Theory and Practice in Adult Learning. 2d ed. Learning Concepts, 1979.
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