Asimov, I. (1989). Frontiers: New discoveries about man and his planet, outer space, and the universe. Plume.
Chicago-viite (17. p.)Asimov, Isaac. Frontiers: New Discoveries About Man and His Planet, Outer Space, and the Universe. New York: Plume, 1989.
MLA-viite (9. p.)Asimov, Isaac. Frontiers: New Discoveries About Man and His Planet, Outer Space, and the Universe. Plume, 1989.
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