Swan, Michael, author
Cambridge University Press, 1993
Buku Teks
Noble, James.
Oliver & Boyd,, 1982.
Buku Teks
Crystal, David, 1941-, author
Cambridge University Press, 1995
Buku Referensi
Sullivan, Patricia Noble, author
Macmillan Company, 1997
Buku Teks
Ceramella, Nick, author
Cambridge university press, 2011
Buku Teks