The average annual return over the period 1926-2009 for the S&P 500 is 11.5%, and the standard deviation of returns is 21%. Based on these numbers, what is a 95% confidence interval for 2010 returns? O A. -10.7%, 32.1% OB. -30.5%, 53.5% O C. -1.5%, 21.4% OD. -30.5%, 74.9%