Howarth, David, author
Edward Elgar, 2013
Buku Teks
Edited by Donald earl childress III
Cambridge University Press, 2014
Buku Teks
Brown, Esther Lucile, author
Russell Sage Foundation, 1948
Buku Teks
Hegland, Kenney
West Pub. Co., 1995
Buku Teks
Hegland, Kenney F., author
Thomson West, 2003
Buku Teks