Young, Arthur, author
Sphere, 1986
Buku Referensi
Durell, William, author
McGraw-Hill, 1985
Buku Teks
Brown, Ronald
Amcom, 1979
Buku Teks
Faguet, Dmitri, author
John Wiley & Sons, 2003
Buku Teks
Haneberg, Lisa, author
American Society for Training & Development, 2007
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