Duke University Press,
Majalah, Jurnal, Buletin
Abel, Darrel, author
Barron's Educational Series, 1963
Buku Referensi
Short, Raymond W., author
Henry Holt and Company, 1954
Buku Teks
Wachner, Clarence W., author
Macmillan, 1963
Buku Teks
United State Information Agency, 1994
Buku Teks