Explain why standard deviation may not be an entirely appropriate measure of risk for purposes of this comparison. $($Select the best answer below.$)$

A$.$ The standard deviation measure fails to take into account both the risk$-$free rate and the return of the investment. Investors would prefer higher return but less volatility, and the coefficient of variation provides a measure that takes into account both aspects of investors' preferences.

B$.$ The standard deviation measure fails to take into account both the volatility and the risk$-$free rate. Investors would prefer higher return but less volatility, and the coefficient of variation provides a measure that takes into account both aspects of investors' preferences.

C$.$ The standard deviation measure fails to take into account both the volatility and the return of the investment. Investors would prefer higher return but less volatility, and the coefficient of variation provides a measure that takes into account both aspects of investors' preferences.

D$.$ The standard deviation measure fails to take into account both the volatility and the return of the investment. Investors would prefer lower return but higher volatility, and the coefficient of variation provides a measure that takes into account both aspects of investors' preferences.