King, Kenneth
Longmann Group, 1991
Buku Teks
Flavin, Christopher
Worldwatch Institute, 1986
Buku Teks
edited by Frances Stewart, Ruhi Saith, Barbara Harriss-White
Palgrave Macmillan, 2007
Buku Teks
Bryant, John
Cornell University Press, 1969
Buku Teks
Kamrava, Mehran
Routledge , 2000
Buku Teks