Kellett, Mary, author
Paul Chapman Publishing, 2005
Buku Teks
Bell, Phillip, author
Sage, 2001
Buku Teks
Drago, Carl, author
Blackwell Publishing, 2007
Buku Referensi
Ziegler, Kathleen, author
Rockport Publishers, 1994
Buku Referensi
Drago, Carl, author
Blackwell, 2014
Buku Teks