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Majalah, Jurnal, Buletin
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Buku Teks
Cassady, Marshall
National Textbook, 1993
Buku Teks
editor, James R. Brandon
Cambridge Unipersity Press, 1993
Buku Referensi
California : The Institute of International Studies, University of California, 1993
Majalah, Jurnal, Buletin