Blair, Walter, author
Scott, Foresman and Company, 1948
Buku Teks
Luecke, Richard A., author
American Management Association, 2008
eBooks
Burt, Angela, author
Stanley Thornes, 1995
Buku Referensi
Evans, David, author
Melbourne University Press, 2002
Buku Teks
Rudd, Robert D., author
Duxbury Press, 1974
Buku Teks