http://owl.english.purdue.edu/owl/resource/591/1/
http://owl.english.purdue.edu/owl/resource/540/1/
http://writing2.richmond.edu/writing/wweb/article.html
http://www.writing.utoronto.ca/images/stories/Documents/articles.pdf
http://www.writing.utoronto.ca/images/stories/Documents/definite-article.pdf
http://www.unc.edu/depts/wcweb/handouts/articles.html
http://www.sass.uottawa.ca/writing/kit/grammar-articles.php