Não informado. (2021). Annual Bulletin of Coal Statistics for Europe and North America. United Nations.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Annual Bulletin of Coal Statistics for Europe and North America. New York: United Nations, 2021.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Annual Bulletin of Coal Statistics for Europe and North America. United Nations, 2021.
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