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Buku Teks SO
McGraw-Hill, [date of publication not identified]
Buku Teks
Genewa : Departemen of Communication and Public Informasi of the ILO, 2006,
Majalah, Jurnal, Buletin
edited by Mona Livholts and Lia Bryant
Routledge, 2017
Buku Teks
edited by William F. Butler, Robert A. Kavesh
Prentice-Hall, 1966
Buku Teks