Keenam, Denis
Pitman, 1993
Buku Teks
Foskett, David, author
Thomson Reuters, 2010
Buku Teks
Keenan, Denis, author
Pearson-Longman, 2002
Buku Teks
Endicott, Timothy, author
Oxford University Press, 2015
Buku Teks
Carvan, John, author
LBC Information Services, 1997
Buku Teks