Heslpo, Brent D., author
Sybex, 1990
Buku Teks
[publisher not identified], [date of publication not identified]
Buku Teks
Birley, Sue, author
Financial Times Prentice Hall, 2000
Buku Teks
Watson, John, author
Macmillan, 1990
Buku Teks
Prentice-Hall, 2002
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