. the graph assumes $ 100 originally invested on september 18 , 2008 , the date upon which our common stock began trading , in each of our series a common stock , series b common stock and series c common stock , the s&p 500 index , and the stock of our peer group companies , including reinvestment of dividends , for the period september 18 , 2008 through december 31 , 2008 and the years ended december 31 , 2009 , 2010 and 2011