Hawken, Paul
Little, Brown and company , 1999
Buku Teks
Hugh L.Evans M.A.
Sweet and Maxwell, 1997
Buku Teks
Roberts, Chris, 1959-, author
Carlton Books, 2014
Buku Referensi
Covell, Charles, author
Macmillan, 1992
Buku Teks
Jackson, Rosemary
Routledge , 1991
Buku Teks