Twomey, David P.
South-Western Publishing Company, 1986
Buku Teks
Mason, Peter, author
Routledge, 1998
Buku Teks
edited by Mark Howard, Roger Masefield ; assistant editor, Jason Chuah
Nexis Butterworths, 2006
Buku Teks
Benjamin, Jane, author
Fourmat Publishing, 1993
Buku Teks
edited by Richard Haigh, Dai Harris
Routledge, 1994
Buku Teks