Perkins, C. (1939). Man's advancing civilization. Rand McNally.
Lua i Stíl Chicago (17ú heag.)Perkins, Clarence. Man's Advancing Civilization. New York, Chicago [etc.]: Rand McNally, 1939.
Lua MLA (9ú heag.)Perkins, Clarence. Man's Advancing Civilization. Rand McNally, 1939.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.