Cita APA (7th ed.)
(1989). The world book encyclopedia of sciene: The planet earth. World Book,Inc.
Cita Chicago (17th ed.)
The World Book Encyclopedia of Sciene: The Planet Earth. Chicago: World Book,Inc, 1989.
Cita MLA (9th ed.)
The World Book Encyclopedia of Sciene: The Planet Earth. World Book,Inc, 1989.
Atenció: Aquestes cites poden no estar 100% correctes.