R.B. Parry, C.R. Perkins, editor
Library Association Publishing, 2001
Buku Teks
Buzan, Tony, author
Wood Lane, 2003
Buku Teks
Kellaway, George P.
Methuen & Co. , 1949
Buku Teks
Ballard, G.A.
London Duckworth 1927
Buku Teks
East, W. Gordon
Methuen, 1950
Buku Teks