Powell, Edward
Oxford University Press, 1989
Buku Teks
Mike Fitzgerald, Gregor McLennan and Jennie Pawson at the Open University.
Routledge in association with Open University Press, 2001
Buku Teks
Rawlings, Philip
Longman, 1999
Buku Teks
Roth, Mitchel P.
Cengage Learning , 2010
Buku Teks
Jones, Mark
Elsevier, 2012
Buku Teks