Griffith, Martin
Routledge, 2002
Buku Teks
edited by Beth A. Simmons and Richard H. Steinberg
Cambridge University Press, 2006
Buku Teks SO
Moon, Parker Thomas
Macmillan, 1926
Buku Referensi
Deutsch, Karl Wolfgang, 1912-1992
Prentice-Hall, 1988
Buku Teks SO
edited by William T.R. Fox
Indiana University of Notre Dame Press , 1959
Buku Teks SO