Atwood, Christee Gabour
ASTD Press, 2007
Buku Teks SO
Haneberg, Lisa
American Society for Training & Development, 2006
eBooks
Gendelman, Joel
ASTD Press, 2010
eBooks
Crosbie, Liz
McGraw-Hill, 1995
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Hagve, D.C.
English Longvage Book Society and Longman Group , 1969
Buku Teks