Shaughnessy, John J., author
McGraw-Hill, 2006
Buku Teks
Langdridge, Darren, author
Pearson, 2004
Buku Teks
Benjafield, John G.
Allyn and Bacon , 1994
Buku Teks
Goodwin, C. James, author
John Wiley & Sons, 2005
Buku Teks
Goodwin, C. James, author
Wiley , 2010
Buku Teks