You find a certain stock that had returns of 4 percent, -5 percent, -15 percent, and 16 percent for four of the last five years. The average return of the stock for the past year-year period was 8 percent. What is the standard deviation of the stock's returns for the 5-year period? A. 21.39 percent B. 24.98 percent C. 27.16 percent D. 21.22 percent E. 34.02 percent.