Johnston, R.J. (Ronald John)
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Buku Teks SO
David J. Bartholomew ... [et.al]
CRC Press, Taylor & Francis Group, 2008
Buku Teks SO
Universitas Indonesia, 2006
UI - Skripsi Membership
Universitas Indonesia, 2007
UI - Skripsi Membership
Forthofer, Ron N., 1944-
Lifetime Learning Publications, 1981
Buku Teks