Gehlen, K. v. (1985). The environmental impacts of exploitation of oil shales and tar sands. United Naions Environment Programme.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रGehlen, K. von. The Environmental Impacts of Exploitation of Oil Shales and Tar Sands. Nairobi: United Naions Environment Programme, 1985.
एमएलए (9वां संस्करण) प्रशस्ति पत्रGehlen, K. von. The Environmental Impacts of Exploitation of Oil Shales and Tar Sands. United Naions Environment Programme, 1985.
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