White, Leonard D.
Macmillan, 1955
Buku Teks
Pritchett, C. Herman
University of North California Press, 1943
Buku Teks SO
Pfiffner, John M.
Ronald Press, 1960
Buku Teks
edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Simon, Herbert A.
Alfred A. Knopf, 1973
Buku Teks