Waterland, Liz
The Thimble Press, 1995
Buku Teks
McRae, John, author
Routledge, 1999
Buku Teks
Anderson, Dee, author
[American Management Association, ], 2009
eBooks
Aukerman, Robert C.
John Wiley & Sons, 1981
Buku Teks
Schumm, Jeanne Shay, author
Freespirit Publishing, 1999
Buku Referensi