Hudson, W. J., author
Sydney University Press, 1970
Buku Teks
Sniderman, Paul M
University of California Press, 1981
Buku Teks
Curtis, Lionel
Macmillan, 1932
Buku Teks
Foreign Languages Press, 1955
Buku Teks
Shank, Patti, author
American Society for Training & Development, 2010
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