Maslen, Andy, author
Marshall Cavendish, 2011
Buku Teks
Keup, Erwin J.
Entrepreneur Press, 2004
Buku Teks
Elliot, Rose, author
Chapmans Publisher Ltd., 1994
Buku Referensi
Entrepreneur Press Rich Mintzer
Entepreneur Press, 2011
Buku Teks
Entrepreneur Press, Cheryl Kimball
Entepreneur Press, 2011
Buku Teks