问题如下：
An analyst gathered the following information about a portfolio’s performance over the past ten years:
If the mean return on the risk-free asset over the same period was 5.0%, the coefficient of variation and Sharpe ratio, respectively, for the portfolio are closest to:
选项：
解释：
C is correct.
The coefficient of variation measures total risk per unit of return or standard deviation/mean return, or 15.7/11.8 = 1.33. The Sharpe ratio is excess return per unit of risk or excess return/standard deviation. The mean excess return is 11.8% − 5.0% = 6.8%, so the Sharpe ratio is 6.8/15.7 = 0.43.
老师您好，题目中的“If the mean return on the risk-free asset over the same period was 5.0%“，我理解成了这个asset是risk-free的，他的mean return是5%，所以sharp ratio我使用5%/15.7%。 请问这个应该怎么理解呀？谢谢
