Cita APA (7th ed.)
Allen, W. L. National Geographic: Vol. 191, no. 2, February 1997. National Geographic Society.
Cita Chicago (17th ed.)
Allen, William L. National Geographic: Vol. 191, No. 2, February 1997. Washington, EUA: National Geographic Society.
Cita MLA (9th ed.)
Allen, William L. National Geographic: Vol. 191, No. 2, February 1997. National Geographic Society.
Atenció: Aquestes cites poden no estar 100% correctes.