(1994). Project learning tree: Environmental education activity guide (2nd.). Project Learning Tree.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रProject Learning Tree: Environmental Education Activity Guide. 2nd. Washington: Project Learning Tree, 1994.
एमएलए (9वां संस्करण) प्रशस्ति पत्रProject Learning Tree: Environmental Education Activity Guide. 2nd. Project Learning Tree, 1994.
चेतावनी: ये उद्धरण हमेशा 100% सटीक नहीं हो सकते हैं.