Express the Product as a Sum Containing Only Sines or Cosines

Multiple Choice

Express the product as a sum containing only sines or cosines.
- $- 2 \sin ( 5 \theta ) \sin \theta$

A) $\cos ( 7 \theta ) - \cos ( 3 \theta )$
B) $\cos ( 6 \theta ) + \cos ( 4 \theta )$
C) $\cos ( 7 \theta ) + \cos ( 3 \theta )$
D) $\cos ( 6 \theta ) - \cos ( 4 \theta )$