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Macmillan, 1967
Buku Teks
Levinson, Charles
George Allen & Uniwin, 1972
Buku Teks
Ellem, Bradon
New South Wales University Press, 1989
Buku Teks
Bussolo, Maurizio
The World Bank, 2009
Buku Teks
Marshall, F. Ray
Ill. Richard D. Irwin , 1980
Buku Teks