World Bank , 1974
Buku Teks
Steven J. Klees, Joel Samoff, Nelly P. Stromquist, editor
[Sense;, ], 2012
eBooks
Gould, W.T.S., author
John Wiley, Longman Scientific, 1993
Buku Teks
edited by Keith Watson
Croom Helm, 1982
Buku Teks
King, Kenneth, author
Longmann Group, 1991
Buku Teks