Tyler, Forrest B.
Plenum Press, 1991
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Pasaribu, Ruth Vania Christine , author
Fakultas Ilmu Pengetahuan dan Budaya Universitas Indonesia, 2014
UI - Skripsi (Membership)
Rose, Peter I., foreword
Random House, 1964
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Schaefer, Richard T, author
Pearson Education, 2015
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Jaret, Charles
Harper Collins College Publishers, 1995
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