Gombas, Pal
Pergamon Press, 1973
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Ida Irma Pratitia R.
Fakultas Psikologi Universitas Indonesia, 2005
UI - Tesis Membership
Khaled Khalaf, Vojkan Vidojkovic, John R. Long, Piet Wambacq
Springer Nature, 2019
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Crain, William C
Prentice-Hall, 2005
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Liptrot, G.F.
The English Language Book Society, 1974
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