Cross, Wilbur
Prentice-Hall, 1995
Buku Referensi
Collin, P. H.
Peter Collin Publishing, 2001
Buku Teks
Greener, Michael
Penguin books, 1994
Buku Referensi
Oxford reference
Oxford University Press, 1990
Buku Referensi
Kurian, George Thomas
[American Management Association, ], 2013
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