George, Stephen
Oxford University Press, 1985
Buku Teks
edited by Stephen White, Judy Batt and Paul G. Lewiss
Macmillan, 1993
Buku Teks SO
Oxford University Press, 2003
Buku Teks SO
Sage, 2010
eBooks
Wiarda, Howard J.
Hartcourt College Publishers, 2001
Buku Teks SO