Buchanan, Robert Angus, author
Penguin, 1972
Buku Teks
McIlroy, John, author
Manchester University Press , 1995
Buku Teks
Richards, Denis, author
Longman, Green, 1952
Buku Teks
Robson, R., author
Macmillan, 1957
Buku Teks
Grove, J.M.
Longmans, 1962
Buku Teks