editor in chief Paul Procter
Cambridge University Press, 1995
Buku Referensi
Lutz, William D., author
Cambridge University Press, 1994
Buku Referensi
Swan, Michael, author
Cambridge University Press, 1987
Buku Teks
edited by Ian Ousby
Cambridge University Press, 1993
Buku Referensi
edited by Ian Qusby
Cambridge University Press, 1988
Buku Referensi