Returns for the Alcoff Company over the last 3 years are shown below. What's the standard deviation of the firm's returns? (Hint: This is a sample, not a complete population, so the sample standard deviation formula should be used.) Year Return 2010 21.00% 2009 12.50% 2008 26.40% Select the correct answer. a. 20.99% b. 21.07% c. 21.03% d. 21.11% e. 21.15%