Hjelte, George
Lea and Febiger, 1978
Buku Teks
Simon, Herbert A., author
Alfred A. Knopf, 1973
Buku Teks
Buku Teks
Bartholomew, Paul C., author
Littlefield, Adams, 1959
Buku Teks
edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks