Smith, Shawn, author
American Management Association, 2004
eBooks
Whiteside, Mike, author
Thorsons, 1991
Buku Teks
Lo, Raymond
Times Books International, 1996
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Tonga Ilbosa, author
Dong-A libo, 2010
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Segal, Inna, author
Atria Paperback, 2010
Buku Teks