Returns for the Dayton 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 2011 21% 2010 -12.50% 2009 25% Answer choices: A. 20.08% B. 20.59% C. 21.11% D. 21.64%