Nicholls, Audrey, author
George Allen and Unwin, 1972
Buku Teks
Grellet, Francoise, author
Cambridge University Press, 1981
Buku Teks
Ronald, Dana M.
John Wiley & Sons, 1987
Buku Teks
United Nations , 1978
Buku Teks
Overfield, Karen, author
American Society for Training & Development, 1997
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