Express as a Sum or Difference $\sin 7 t \sin 2 t$

Multiple Choice

Express as a sum or difference. $\sin 7 t \sin 2 t$

A) $\cos ( 5 t ) - \cos ( 9 t )$
B) $\frac { 1 } { 2 } \cos ( 6 t ) - \frac { 1 } { 2 } \cos ( 10 t )$
C) $\sin ( 5 t ) - \sin ( 9 t )$
D) $\frac { 1 } { 2 } \cos ( 5 t ) - \frac { 1 } { 2 } \cos ( 9 t )$
E) $\frac { 1 } { 2 } \sin ( 5 t ) - \frac { 1 } { 2 } \sin ( 9 t )$