Richards, Jack C., author
Cambridge University Press, 2005
Buku Teks
World Health Organization, 1996
Buku Teks
Frieman, Barry B., author
McGraw-Hill, 2001
Buku Teks
Baker, Colin, author
Multilingual Matters Ltd, 1995
Buku Teks
Ur, Penny, author
Cambridge University Press, 1988
Buku Teks