Cita APA (7th ed.)

Roberts, J. M. (2000). Twentieth century: The history of the world, 1901 to 2000. Penguin Books.

Cita Chicago (17th ed.)

Roberts, J. M. Twentieth Century: The History of the World, 1901 to 2000. New York: Penguin Books, 2000.

Cita MLA (9th ed.)

Roberts, J. M. Twentieth Century: The History of the World, 1901 to 2000. Penguin Books, 2000.