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McGraw-Hill, 1994
Buku Referensi
Cortada, James W., author
McGraw-Hill, 2000
Buku Referensi
Library Association Publishing, 1994
Buku Referensi
Europa Publications Limited, 1993
Buku Referensi
United Nation. Departement of Economic and Social Affairs. Statistical Office
United Nation, 1957
Buku Referensi