Atwood, Christee Gabour
ASTD Press, 2007
Buku Teks
Byham, William C.
FT Press , 2002
Buku Teks
Hutley, F.C. (Francis Charles)
Law Book, Co., 1975
Buku Teks
Bower, Marvin
Massachutts Harvard University Press , 1949
Buku Teks
Gardner, John, author
Macmillan, 1982
Buku Teks