Boyd, Claire, author
Wiley Blackwell, 2014
Buku Teks
editor, Owen Hargie
New York , 2006
Buku Referensi
Johnson, Stuart, author
Oxford Univesity Press, 2009
Buku Teks
John Wiley & Sons, 1999
Buku Teks
McEwen, Abayomi, author
McGraw-hill Open Univer, 2011
Buku Teks