Express the Product as a Sum or Difference $\sin 3 x \sin 7 x$

Multiple Choice

Express the product as a sum or difference.
- $\sin 3 x \sin 7 x$

A) $\frac { 1 } { 2 } ( \cos 4 x - \cos 10 x )$
B) $\frac { 1 } { 2 } ( \cos 10 x - \sin 4 x )$
C) $\frac { 1 } { 2 } ( - \cos 4 x - \cos 10 x )$
D) $\sin ^ { 2 } 21 x ^ { 2 }$