Jeff decided to accept the risk and purchased a high growth stock. His returns for the past six years were 34 percent, 25 percent, -40 percent, 30 percent, -15 percent and 20 percent. What is the standard deviation of these returns? (SHOW CALCULATION)

A. 6.46 percent

B. 8.84 percent

C. 29.73 percent

D. 44.20 percent

E. 56.15 percent