Ur, Penny, author
Cambridge University Press, 1999
Buku Referensi
Rivers, Wilga M., author
Cambridge University Press, 1994
Buku Teks
edited by Valerie Kinsella
Cambridge Uniiversity Press , 1979
Buku Teks
Richards, Jack C., author
Cambridge University Press, 1994
Buku Teks
Rivers, Wilga M., author
Cambridge University Press, 1985
Buku Teks