Select the Function That Is Equivalent To $f(x)=\sin 7 x-\sin 11 x$

Multiple Choice

Select the function that is equivalent to $f(x) =\sin 7 x-\sin 11 x$ .

A) $f(x) =2 \sin 9 x \cos 2 x$
B) $f(x) =-2 \sin 9 x \cos 2 x$
C) $f(x) =-2 \cos 9 x \sin 2 x$
D) $f(x) =2 \cos 9 x \sin 2 x$