APA (7e ed.) Bronvermelding

Não informado. (1931). International coal trade. U.S. Department of the Interior, Bureau of Mines.

Chicago (17e ed.) Bronvermelding

Não informado. International Coal Trade. Washington: U.S. Department of the Interior, Bureau of Mines, 1931.

MLA (8e ed.) Bronvermelding

Não informado. International Coal Trade. U.S. Department of the Interior, Bureau of Mines, 1931.

Let op: Deze citaties zijn niet altijd 100% accuraat.