Não informado. (1968). Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Annual Bulletin of General Energy Statistics for Europe. New York: United Nations, Economic Commission for Europe, 1968.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe, 1968.
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