Não informado. (1991). Research and Exploration. National Geographic Society.
Style de citation Chicago (17e éd.)Não informado. Research and Exploration. Gaithersburg, Md: National Geographic Society, 1991.
Style de citation MLA (8e éd.)Não informado. Research and Exploration. National Geographic Society, 1991.
Attention : ces citations peuvent ne pas être correctes à 100%.