McGivering, Ian C.
Liverpool University Press, 1960
Buku Teks
Child, John, author
George Allen and Unwin, 1969
Buku Teks
Jordan, Peter, author
Gower , 1995
Buku Teks
consultant editor, Michael Armstrong
AP Information Services, 1997
Buku Referensi
Jones, Noragh, author
Gower, 1987
Buku Teks