Paris : The United Nations Educational
Majalah, Jurnal, Buletin
Mancuso, Joseph
Simon & Schuster , 1993
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Sandler, Corey
Prentice-Hall, 2001
Buku Teks
Gookin, Dan
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Buku Teks
edited by William M. Lafferty and James Meadowcroft
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Buku Teks