Fisher, R. (1991). Heartland of a continent: America's plains and prairies. National Geographic Society.
Lua i Stíl Chicago (17ú heag.)Fisher, Ron. Heartland of a Continent: America's Plains and Prairies. Washington, D.C.: National Geographic Society, 1991.
Lua MLA (9ú heag.)Fisher, Ron. Heartland of a Continent: America's Plains and Prairies. National Geographic Society, 1991.
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