Chapman, Brian
Allen & Unwin, 1966
Buku Teks
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
Pfiffner, John M., author
Ronald Press, 1960
Buku Teks
edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Simon, Herbert A., author
Alfred A. Knopf, 1973
Buku Teks