Which of the following subnet masks are classful?

Question $2$ options:

$255\mathrm{.}255\mathrm{.}255\mathrm{.}0$

$255\mathrm{.}255\mathrm{.}192\mathrm{.}0$

$255\mathrm{.}0\mathrm{.}0\mathrm{.}0$

$255\mathrm{.}255\mathrm{.}255\mathrm{.}240$

$255\mathrm{.}255\mathrm{.}0\mathrm{.}0$