Wessels, Dieter, author
Macmillan, 1992
Buku Teks
edited by Stephen Clarke
Harper Collins, 1995
Buku Referensi
Shaw, Gisela, author
Hodder & Stoughton, 1995
Buku Referensi
Woodhall, Victoria
Hodder & Stoughton, 1992
Buku Teks
McKeane, Alasdair, author
Longman, 1994
Buku Teks