Cita APA (7a ed.)
Allen, W. L. National Geographic: Vol. 191, no. 1, January 1997. National Geographic Society.
Cita estilo Chicago (17a ed.)
Allen, William L. National Geographic: Vol. 191, No. 1, January 1997. Washington, EUA: National Geographic Society.
Cita MLA (9a ed.)
Allen, William L. National Geographic: Vol. 191, No. 1, January 1997. National Geographic Society.
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