Priestley, John Boynton, 1894-1984
Garden City Books, 1959
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Christian Baumgartner , Martin Uitz, Karl Krainer, Peter Hasslacher
The Federal Press Service, 2002
Buku Referensi
London : Routledge
Majalah, Jurnal, Buletin
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Timothy Insoll
Routledge, 2001
Buku Teks SO