Merriam-Webster, Inc., 1988
Buku Teks
Wilson, Kevin, 1958- , author
[American Management Association;, ], 2011
eBooks
Wilson, Kevin, 1958- , author
American Management Association;, 2010
eBooks
Merriam-Webster's, Incorporated, 1993
Buku Referensi
Treece, Malra, author
Allyn and Bacon, 1989
Buku Teks