$\sin 65^{\circ}+\cos 65^{\circ}=?$

$\frac{\sqrt{3}}{2} \cos 40^{\circ}$

$\frac{1}{2} \sin 20^{\circ}$

$\frac{\sqrt{3}}{2} \sin 40^{\circ}$

$\sqrt{2} \cos 20^{\circ}$