Cooper, Phillip J., author
Thomson Wadsworth, 2005
Buku Teks
Le Sueur, A.P. (Andrew P.), author
Oxford University Press, 2013
Buku Teks
Raymond W. Cox III
Routledge, 2009
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