Weigle, Sara Chusing
Cambridge University Press, 2002
Buku Teks
Little, Brown And Company, 1982
Koleksi Publik
John Hartley [and others]
Rinehart and Winston, 1962
Buku Teks
Kirk, Ken, author
American Society for Training & Development, 2010
eBooks
Bogg, Daisy, author
McGraw-Hill, 2012
Buku Teks