Yerbury, Hilary
University of Technology, 1992
Buku Referensi
Indiana Purdue University Press, 2014
Buku Teks
Evans, G. Edward, 1937-
Neal-Schuman, 2013
Buku Teks
McLeod, John
McGraw-hill Open University press, 2012
Buku Teks
Norman, Sandy
Facet Publishing, 2004
Buku Teks