Cita APA (7th ed.)
Graves, W. National Geographic: Vol. 178, no. 1, July 1990. National Geographic Society.
Cita Chicago (17th ed.)
Graves, William. National Geographic: Vol. 178, No. 1, July 1990. Washington, EUA: National Geographic Society.
Cita MLA (9th ed.)
Graves, William. National Geographic: Vol. 178, No. 1, July 1990. National Geographic Society.
Atenció: Aquestes cites poden no estar 100% correctes.