Rosen, Harvey S., author
McGraw-Hill, 2010
Buku Teks
edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Pfiffner, John M., author
Ronald Press, 1960
Buku Teks
Denhardt, Robert B., author
Harcourt College, 1999
Buku Teks
McMenemy, David, author
Facet, 2009
Buku Teks