Which of the following triatomic molecule(s) will behave as diatomic molecule for consideration of degrees of freedom?

The correct option is A $C{O}_2$
$C{O}_2$ is a triatomic linear molecule, and in the case of triatomic molecule of linear type, there are only two rotational degrees of freedom. It, therefore, behaves like a diamotic molecule.
$H_{2}O$ and $S{O}_2$ molecules are non-linear and hence would have three rotational degrees of freedom.