edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Denhardt, Robert B., author
Harcourt College, 1999
Buku Teks
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
Denhardt, Robert B., author
Thomson, 2009
Buku Teks
Nigro, Felix A., author
Harper and Row , 1977
Buku Teks