Identify the one true statement about an optimal $($efficient$)$ portfolio :

$($A$)$ The ratio of a stock' s expected excess return and its variance is equal

across all stocks in the portfolio $.$

$($B$)$ The ratio of a stock' s expected excess return and its covariance with

any other risky asset is the same across all stocks $.$

$($C$)$ The ratio of a stock $\text{'}$s expected excess return and its covariance with

the portfolio must not be equal across all stocks $.$

$($D$)$ The ratio between the investor's risk aversion and the stock's

expected excess return is the same across all stocks $.$

$($E$)$ None of the above $.$