edited by Richard M. Ludwig, Clifford A. Nault
Oxford University Press , 1986
Buku Referensi
Abel, Darrel, author
Barron's Educational Series, 1963
Buku Referensi
Duke University Press,
Majalah, Jurnal, Buletin
United State Information Agency, 1994
Buku Teks
Hart, James, author
Oxford University Press, 1965
Buku Referensi