Nugent, Neill
Macmillan, 1994
Buku Teks
Oxford University Press, 2003
Buku Teks
Cini, Michelle
Oxford Univesity Press, 2010
Buku Teks
George, Stephen
Oxford University Press, 1985
Buku Teks
edited by Jolyon Howorth and Anand Menon
Routledge, 1997
Buku Teks