The average annual return over the period 1926-2009 for the S&P 500 is 11.3%, and the standard deviation of returns is 21.7%. Based on these numbers, what is a 67% confidence interval for 2010 returns? OA. - 31.2%, 52.8% B. - 1.6%, 19.8% C. - 10.4%, 33% D.-31.2%, 46.2%