Write the Sum as a Product $\sin 4 x + \sin 5 x$

Multiple Choice

Write the sum as a product. $\sin 4 x + \sin 5 x$

A) $\sin 4 x \sin 5 x$
B) $\sin 4 x \cos 5 x$
C) $2 \sin ( 9 x / 2 ) \cos ( x / 2 )$
D) $\sin 4 x \cos ( x / 2 )$
E) $2 \sin 3 x \cos ( x / 2 )$