Bear, Mariah, author
McGraw-Hill , 2000
Buku Teks
Bear, Mariah
Berkeley McGraw-Hill 2000,
Buku Referensi
Clinton, Chelsea, author
Listening Library , 2015
Buku Teks
Terwelp, Wendy, author
American Society for Training & Development, 2011
eBooks
Garbutt, Douglas, author
Pustaka Binaman Pressindo, 1994
Buku Referensi