Bruce, R. Robert
Hodder & Stoughton, 1994
Buku Teks
Bhatia, Tej K.
Routledge, 2000
Buku Teks SO
Coultas, Barbara
Teach Yourself Books, 1990
Buku Teks SO
Graham, Gaelle
Hodder & Stoughton, 1991
Buku Teks SO
Wilkes, Angela
Passport Books, [Date of publication not identified]
Buku Teks SO