Talbot, Phillips
Harper and Brothers, 1958
Buku Teks SO
Griffith, Martin
Routledge, 2002
Buku Teks
edited by Beth A. Simmons and Richard H. Steinberg
Cambridge University Press, 2006
Buku Teks SO
Bombay : Oxford Universty Press
Majalah, Jurnal, Buletin
Rosinger, Lawrence K.
Macmillan, 1950
Buku Teks SO