(2018). National geographic almanac 2019: Hot new science, incredible photographs, maps, facts, infographics & more (U.S. edition.). National Geographic.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNational Geographic Almanac 2019: Hot New Science, Incredible Photographs, Maps, Facts, Infographics & More. U.S. edition. Washington, D.C.: National Geographic, 2018.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNational Geographic Almanac 2019: Hot New Science, Incredible Photographs, Maps, Facts, Infographics & More. U.S. edition. National Geographic, 2018.
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