Henderson, David, author
New Zealand Business Roundtable , 1998
Buku Teks
Hudson, Ray, author
Prentice-Hall, 2000
Buku Teks
Young, Katherine G., author
Oxford University Press, 2014
Buku Teks
Cambridge University Press, 2019
eBooks
Tucker, W.T., author
Holt, Renehart and Winston, 1964
Buku Teks