Hudson, John, author
Longman, 1996
Buku Teks
Bauer, Laurie
Cambridge Cambridge University Press 1983
Buku Teks
Bauer, Laurie, author
Cambridge University Press, 2012
eBooks
Slapper, Gary, author
Cavendish Publishing Limited, 2000
Buku Teks
Keenan, Denis, author
Pitman, 1992
Buku Teks