Cambridge Hobsons 1987
Buku Referensi
Osaka : Graduate School of Human Sciences Osaka University
Majalah, Jurnal, Buletin
Henderson, Algo D., author
Unesco Paris, 1970
Buku Referensi
Cass, James, author
New York, Harper & Row Publishers
Buku Referensi
Frederick, Robert W.
USA Appleton 1947
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