An investor can design a risky portfolio based on two stocks, A and B. Stock A has an expected return of 18% and a standard deviation of return of 20%. Stock B has an expected return of 14% and a standard deviation of return of 5%. The correlation coefficient between the returns of A and B is 0.50. The risk-free rate of return is 10%. The standard deviation of return on the optimal risky portfolio is __________.

A. 5%

B. 11.5%

C. 10%

D. 0%

E. 8%