Hauck, Hazel M.
Cornell University, 1958
Buku Teks SO
Rice, E.B.
World Bank, 1997
Buku Teks SO
Dobby, Ernest Henry George, 1906-1981
University of London Press, 1950
Buku Teks
Dobby, Ernest Henry George, 1906-1981
University of London Press, 1953
Buku Teks SO
Henderson, William
MIT Press, 1963
Buku Teks SO