Standard deviation and expected return information for four investments selling for the same price is as

Standard deviation and expected return information for four investments selling for the same price is as follows:

Investment Standard Deviation Expected Return
O A 25% 20%
O B 20% 18%
O C 12% 8%
O D 10% 10%

What investment is the best choice in terms of the risk/return relationship?

Please provide the calculation for each of the four options and the reference source