APA
William L. Allen, . (2001). National Geographic. 1145 17th Street, NW Wasihington DC200364688: National Geographic Society.
Chicago
William L. Allen, . 2001. National Geographic. 1145 17th Street, NW Wasihington DC200364688: National Geographic Society.
Harvard
William L. Allen, . (2001). National Geographic. 1145 17th Street, NW Wasihington DC200364688: National Geographic Society.
MLA
William L. Allen, . National Geographic. 1145 17th Street, NW Wasihington DC200364688: National Geographic Society. 2001.