Dubois, Brenda, 1949-
Allyn and Boston, 1992
Buku Teks
Gore, M.S.
Asia Publishing House, 1965
Buku Teks SO
Cohen, Nathan Edward
National Ass. of Workker, 1964
Buku Teks SO
Genewa : Departemen of Communication and Public Informasi of the ILO, 2006,
Majalah, Jurnal, Buletin
edited by Tony Tripodi ... [and others]
F.E. Peacock, 1977
Buku Teks SO