Hart, James D., author
Oxford University Press, 1986
Buku Referensi
Watt, Homer A., author
Scott, Foresman and company , 1925
Buku Teks
United State Information Agency, 1994
Buku Teks
Hart, James, author
Oxford University Press, 1965
Buku Referensi
edited by Robert Richards
Littlefield, Adams, 1955
Buku Referensi