Não informado. (2021). Farm Economics. Pennsylvannia State University, Cooperative Extension Service.
Lua i Stíl Chicago (17ú heag.)Não informado. Farm Economics. University Park, Pa: Pennsylvannia State University, Cooperative Extension Service, 2021.
Lua MLA (8ú heag.)Não informado. Farm Economics. Pennsylvannia State University, Cooperative Extension Service, 2021.
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