Evaluating Risk-Adjusted Performance of a Mutual Fund

Consider a mutual fund that has produced an annual return of 12% over the past three years. During this period, the risk-free rate was consistently 2%, and the standard deviation of the fund's returns was 10%. The fund manager claims that the fund has outperformed the market on a risk-adjusted basis. Which of the following metrics is most appropriate to evaluate the fund's risk-adjusted performance in this context?