Não informado. (1960). Educators Guide to Free Science Materials. Educators Progress Service.
Style de citation Chicago (17e éd.)Não informado. Educators Guide to Free Science Materials. Randolph, Wis: Educators Progress Service, 1960.
Style de citation MLA (8e éd.)Não informado. Educators Guide to Free Science Materials. Educators Progress Service, 1960.
Attention : ces citations peuvent ne pas être correctes à 100%.