edited by J. Graham Beaumont
Grange Books, 1989
Buku Referensi
Levitin, Daniel J.
Dutton, 2006
Buku Teks SO
Lucas, Bob
American Management Association, 2008
eBooks
Atkins, Robert C. [Robert Charles], 1944-
Pocket Books, 2002
Buku Teks SO
Brogan, Kelly
Thorson, 2016
Buku Teks SO