Campbell-Kelly, Martin, author
Clarendon Press, 1989
Buku Teks
Harvard Business School, 2009
Majalah, Jurnal, Buletin
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Prentice-Hall, 1972
Buku Teks
Sharma, R.C., author
Tata McGraw-Hill, 2002
Buku Teks
Morrisey, George L., author
Addison-Wesley, 1987
Buku Teks