Which declaration gives the div a bottom, red, $2\mathrm{.}5$ pixels wide, double border?

div $\{$

border$-$bottom: $2\mathrm{.}5px$ double red;

$\}$

border: $2\mathrm{.}5px$ double red;

$\}$

bottom: $2\mathrm{.}5px$ double$-$border red;

$\}$

borderbottom: $2\mathrm{.}5px$ double red;

$\}$