Cita APA (7a ed.)
Allen, W. L. National Geographic: Vol. 196, no. 6, December 1999. National Geographic Society.
Cita estilo Chicago (17a ed.)
Allen, William L. National Geographic: Vol. 196, No. 6, December 1999. Washington, EUA: National Geographic Society.
Cita MLA (9a ed.)
Allen, William L. National Geographic: Vol. 196, No. 6, December 1999. National Geographic Society.
警告：这些引文格式不一定是100％准确.