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
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
Cooper, Phillip J., author
Thomson Wadsworth, 2005
Buku Teks