Marie Curie and other scientists discovered that

the answer is use of support  

naturalization is the process of gaining united states citizenship. becoming an american citizen is the ultimate goal for many immigrants, but very few people are aware that the requirements for naturalization have been over 200 years in the making.

i do not have access to the graph, but from 2001 to 2011 the rate of unemployment in the united states changed drastically. it remained relatively steady, at 5 percent, on average (4.4 percent in 2006 due to the economic expansion and 6 percent in 2002 as a result of the elevated costs of the war of terror) until 2008. it was then when the financial crisis, the worst since the great depression of 1929, occurred. during the recession that followed, the unemployment rate reached almost 10 percent in 2009, and in 2010 it was above 9 percent. by 2011 job losses had been continuous and prolonged for months, but the rate decreased timidly.