Waldholz, Michael
Simon & Schuster , 1997
Buku Teks
Weiss, Marisa C., author
Times Books , 1998
Buku Teks
Moon, Glenn W., author
Holt, Rinehart and Winston, 1964
Buku Teks
Murphy, Tom, author
American Management Association, 2007
eBooks
edited by Penny Kaganoff and Susan Spano
Harcourt Brace & Company, 1997
Buku Teks