Ferris, Brian
Hulton Educational Publications, 1973
Buku Teks
Karpinski, Andrzej
Polonia Publishing House, 1960
Buku Teks
United Nations, 1979
Buku Teks
Chase, Harold W.
Crowell, 1964
Buku Teks
Kuznets, Simon Smith, 1901-
W.W. Norton&Company-Inc, 1965
Buku Teks