Sources

http://www.immigrationpolicy.org/just-facts/how-united-states-immigration-system-works-fact-sheet

http://www.nytimes.com/2010/04/24/us/politics/24immig.html

http://www.msnbc.msn.com/id/38961638/ns/us_news-immigration_a_nation_divided/

http://www.msnbc.msn.com/id/38961638/ns/us_news-immigration_a_nation_divided/