Não informado. (1960). Educators Guide to Free Science Materials. Educators Progress Service.
Cita Chicago Style (17a ed.)Não informado. Educators Guide to Free Science Materials. Randolph, Wis: Educators Progress Service, 1960.
Cita MLA (8a ed.)Não informado. Educators Guide to Free Science Materials. Educators Progress Service, 1960.
Precaución: Estas citas no son 100% exactas.