Ager, D. E., author
Cambridge University Press, 1990
Buku Teks
Ball, Rodney
Routledge, 1997
Buku Teks
Coultas, Barbara, author
Teach Yourself Books, 1990
Buku Teks
Bower, Malcolm
Hodder & Stoughton, 1977
Buku Teks
Barbour, Stephen
Cambridge [England]; New York Cambridge University Press 1990,
Buku Teks