Não informado. (1968). Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe.
Lua i Stíl Chicago (17ú heag.)Não informado. Annual Bulletin of General Energy Statistics for Europe. New York: United Nations, Economic Commission for Europe, 1968.
Lua MLA (8ú heag.)Não informado. Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe, 1968.
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