Paul C. Adams, Julie Cupples, Kevin Glynn, André Jansson and Shaun Moores, authors
Routledge, 2017
Buku Teks SO
Fuchs, Christian
Sage Publications, 2014
eBooks
Rayner, Philip, 1947-
Routledge , 2001
Buku Teks
Wilson, Stan Le Roy
McGraw-Hill, 1995
Buku Teks
Hiebert, Ray Eldon
Longman, 1985
Buku Teks SO