In the case of univariate kernel density estimation, the optimal asymptotic order of the bandwidth is

Please select the correct option.

$O(n^{-\frac{1}{5}})$

$O(n^{-\frac{1}{4}})$

$O(n^{-\frac{1}{2}})$

$O(n^{-\frac{4}{5}})$