Artikel Jurnal
Chalmers, A.F.
University of Green Sland Press, 1982
Buku Teks SO
Trese, Leo J.
Notre Dame, 1964
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Teresa Stoppani, Giorgio Ponzo, George Themistokleous.
Routledge, 2017
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Hwang, Soon-Won
Jimoondang Publishing Company, 2003
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