Zlatova, Y., author
Foreign Languages Publishing House , 1959
Buku Teks
Dacey, John S., author
McGraw-Hill, 2002
Buku Teks
Gillespie, Sheena, author
Allyn and Bacon , 1994
Buku Teks
Rowe, Kim A., author
American Society for Training & Development, 2010
eBooks
Vinson, Betsy Partin, author
Delmar Cengage Learning, 2012
Buku Teks