Wong, David S.Y.
Singapore University Press, 1975
Buku Teks
Hooker, M. B., author
Oxford University Press, 1976
Buku Teks
Neale, Walter C., author
Yale University Press, 1962
Buku Teks
Hooker, M. B., author
Oxford University Press , 1972
Buku Teks
United Nations, 1979
Buku Teks