APA (7e ed.) Bronvermelding

Não informado. (1977). Coal Abstracts. IEA Coal Research.

Chicago (17e ed.) Bronvermelding

Não informado. Coal Abstracts. London: IEA Coal Research, 1977.

MLA (8e ed.) Bronvermelding

Não informado. Coal Abstracts. IEA Coal Research, 1977.

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