Express the Sum or Difference as a Product $\cos 8 x - \cos 4 x$

Multiple Choice

Express the sum or difference as a product.
- $\cos 8 x - \cos 4 x$

A) $- 2 \sin 6 x \sin 2 x$
B) $2 \cos 6 x \cos 2 x$
C) $- 2 \cos 6 x \sin 2 x$
D) $2 \cos 2 x$