United States. Central Intelligence Agency
Macmillan, 1993
Buku Referensi
Routledge, 1992
Buku Teks
University of Technology Sydney
Lovell Johns , 1996
Buku Referensi
editorial information compiled by the Economist
The Economist Newspaper Limited, 1984
Buku Referensi
MacKay, R.A., author
The Ryerson Press, 1935
Buku Teks