Which expression is equal to $\cos 50^{\circ} ?$
A. $\sin 20^{\circ} \cos 30^{\circ}+\cos 20^{\circ} \sin 30^{\circ} \quad$ B. $\sin 20^{\circ} \cos 30^{\circ}-\cos 20^{\circ}-\cos 20^{\circ} \sin 30^{\circ}$
$\mathrm{C} \cdot \cos 20^{\circ} \cos 30^{\circ}+\sin 20^{\circ} \sin 30^{\circ} \quad$ D. $\cos 20^{\circ} \cos 30^{\circ}-\sin 20^{\circ} \sin 30^{\circ}$