Walsh, William J., author
Skyhorse Publishing, 2014
Buku Teks
Clutterbuck, David, 1947-, author
Crest Publishing House, 1999
Buku Teks
Coon, Horace
Signet Key Book, 1962
Buku Teks
Lange, Heinz, author
Abacus, , 2000
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Betof, Edward, author
American Society for Training & Development, 2009
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