Kpedekpo, G.M.K.
Heinemann, 1982
Buku Teks
Doob, Leonard William, 1909-, author
Yale University Press, 1961
Buku Teks
Moore, Clark D
Praeger, 1968
Buku Teks
edited Iman G. Lanti, Greg Mils, Sigit Wardono
Pustaka Cidesindo, 1997
Buku Teks
Amoo, Sam G.
United Nations Development Programme, 1997
Buku Teks