Ackerman, Joseph
Washington, D.C. Resources for the Future c. 1962,
Buku Teks
Ackerman, Joseph
Washington, D>C. Resources for the Future c. 1961,
Buku Teks
Mass John Hopkins , 1965
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Clawson, Marion
Praeger Publishers, 1971
Buku Teks
Unesco, 1981
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