Swan, Michael, author
Oxford University Press, 1995
Buku Teks
edited by Tim Storrie and James Matson
Cassell , 1991
Buku Teks
Howard, Godfrey, author
Pan Macmillan Publishers, 1993
Buku Referensi
Peters, Pam, author
Cambridge University Press, 2006
Buku Referensi
Stone, Linton
Macmillan, 1970
Buku Teks