World Bank
Oxford University Press, 1992
Buku Teks
Mason, Edward S., author
Fordham University Press, 1958
Buku Teks
Weiss, John, author
Prentice-Hall, 1995
Buku Teks
Waterston, Albert, author
John Hopkins University Press, 1969
Buku Teks
Schalkwyk, Herman D. van, editor
[, Wageningen Academic], 2012
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