Henderson, Algo D.
Unesco Paris, 1970
Buku Referensi
Winter, Richard
London: The Falmer Press, 1996
Buku Teks
Organization for Economic Co-operation and Development , 1972
Buku Teks
Hussain, K.M.
Organization for Economic Co-operation and Development , 1976
Buku Teks
UNESCO-UNEP International, 1983
Buku Teks