Ur, Penny, author
Cambridge University Press, 1988
Buku Teks
Wallace, Michael J., author
Cambridge University Press, 2004
Buku Teks
Allwright, Dick, author
Longman, 1993
Buku Teks
Davis, Paul, author
Cambridge University Press, 1994
Buku Teks
Tsui, Amy B. M., author
Cambridge University Press, 2003
Buku Teks