edited by J.M. Porter
Chatam House, 1984
Buku Teks
Fedrizzi, Mariann
South Western Cengage Learning, 2011
Buku Teks
edited by Keith Hancock
Cambridge University Press, 1989
Buku Teks SO
Longman , 1999
Buku Teks
edited by Steve Fleetwood
Routledge, 1999
Buku Teks