IInvestments a and B Both Offer an Expected Rate of Return

IInvestments A and B both offer an expected rate of return of 12.The standard deviation of A is 30 percent and that of B is 20 percent.If an investor wishes to invest in either A or B, then the investor should

A) prefer A to B.
B) prefer B to A.
C) prefer a portfolio including both A and B.
D) The answer cannot be determined without knowing investors' risk preferences.