Her Majesty's Stationery Office, 1955
Buku Teks
Bromhead, Peter
Longman, 1992
Buku Teks
Chapman, Richard A., author
Constable, 1970
Buku Teks
Gilliat-Ray, Sophie, author
Cambridge University Press, 2010
Buku Teks
Buchanan, Robert Angus, author
Penguin, 1972
Buku Teks