19. Which of the following risk-return combinations is the most efficient? Assume Rf = 0%. A. Expected return = 11%, standard deviation = 12% B. Expected return = 12%, standard deviation = 14% C. Expected return = 14%, standard deviation 18% D. Expected return = 17%, standard deviation = 21% A B D R 11% 12% 14% 17% St.D. 12% 14% 18% 21%