单选题 Bill Adams wants to diversify his portfolio by adding certain assets that he expects to lower the overall standard deviation of his portfolio. After selecting several different asset classes. Adams constructed an efficient frontier using various combinations of the assets. Adams can choose a portfolio on the efficient frontier and achieve a diversified investment assuming all of the following assumptions are true, EXCEPT: A. investors believe all investments are represented by a probability distribution of expected returns and seek diversification based on the variability of expected returns. B. investors base investment decisions solely on the expected risk of the investment. C. investor utility curves exhibit diminishing marginal utility of wealth.