Whitney, D. C., & Whitney, R. V. (1990). The American presidents (7th ed.). Prentice Hall Press.
Dyfyniad Arddull ChicagoWhitney, David C., and Robin Vaughn Whitney. The American Presidents. 7th ed. New York: Prentice Hall Press, 1990.
Dyfyniad MLAWhitney, David C., and Robin Vaughn Whitney. The American Presidents. 7th ed. Prentice Hall Press, 1990.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.