Littlejohn, Stephen W., author
Scott, Foresman and Company, 1987
Buku Teks
Bettinghaus, Erwin P., author
Holt, Rinehart and Winston, Inc., 1968
Buku Teks
Ulanoff, Stanley M.
Hastings House, 1977.
Buku Teks
Ulanoff, Stanley M.
Hastings House , 1977
Buku Teks
Sant, Tom, author
American Management Association, 2004
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