Não informado. (1931). International coal trade. U.S. Department of the Interior, Bureau of Mines.
Style de citation Chicago (17e éd.)Não informado. International Coal Trade. Washington: U.S. Department of the Interior, Bureau of Mines, 1931.
Style de citation MLA (8e éd.)Não informado. International Coal Trade. U.S. Department of the Interior, Bureau of Mines, 1931.
Attention : ces citations peuvent ne pas être correctes à 100%.