Dietrich, Ethel B.
Henry Holt and Company, 1940
Buku Teks
Department of Economic Affairs, 1953
Buku Teks
Viner, Jacob, author
George Allen and Unwin, 1960
Buku Teks
Horn, Paul V., author
Prentice-Hall, 1959
Buku Teks
Huges, Helen
Johns Hopkins Univesity Press , 1973
Buku Teks