Cita APA (7th ed.)
Graves, W. National Geographic: Vol. 180, no. 6, December 1991. National Geographic Society.
Cita Chicago (17th ed.)
Graves, William. National Geographic: Vol. 180, No. 6, December 1991. Washington, EUA: National Geographic Society.
Cita MLA (9th ed.)
Graves, William. National Geographic: Vol. 180, No. 6, December 1991. National Geographic Society.
Atenció: Aquestes cites poden no estar 100% correctes.