Willmore, Job, author
American Society for Training & Development, 2009
eBooks
Marianne Wait, editor
Reader's Digest, 2007
Buku Teks
McBride, John, author
BBC Books , 1996
Buku Teks
Mann, Thomas, author
Vintage International , 1995
Buku Teks
Lindsay, Norman, author
Angus & Robertson Publishers, 1918
Buku Teks