Minkov, Michael
Sage, 2013
Buku Teks SO
Finer, S.E.
Clarendon Press Oxford, 1995
Buku Teks
by Jack Bavington
Maclean-Hunter Learning Materials, 1976
Buku Teks SO
Downs, James F.
Glencoe Press, 1975
Buku Teks SO
Mort, Frank
Routledge, 1996
Buku Teks SO