Colton, J. G. (1980). Twentieth century (Rev. ed.). Time-Life Books.
Lua i Stíl Chicago (17ú heag.)Colton, Joel G. Twentieth Century. Rev. ed. Alexandria, Va: Time-Life Books, 1980.
Lua MLA (9ú heag.)Colton, Joel G. Twentieth Century. Rev. ed. Time-Life Books, 1980.
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