Rewrite the Following as a Product of Trigonometric Functions $\cos ( - x ) \cos x - \sin ( - x ) \sin x$

Multiple Choice

Rewrite the following as a product of trigonometric functions.
- $\cos ( - x ) \cos x - \sin ( - x ) \sin x$

A) 1
B) 2
C) $\cos ^ { 2 } x \sin ^ { 2 } x$
D) 0