Artikel Jurnal
Jossey - Bass Publishers , 1996
Buku Teks
Ferguson, Gibson, author
Edinburgh University Press, 2006
Buku Teks
Coverdale, G.M.
Unesco, International Institute for Educational Planning , 1974
Buku Teks
William Wrenall, Quarterman Lee, editors in chief
McGraw-Hill, 1994
Buku Referensi