Não informado. (1974). Coal and Energy Quarterly. National Coal Board.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Coal and Energy Quarterly. London: National Coal Board, 1974.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Coal and Energy Quarterly. National Coal Board, 1974.
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