Select the Function That Is Equivalent To $f(x)=\cos 5 x+\cos 11 x$

Multiple Choice

Select the function that is equivalent to $f(x) =\cos 5 x+\cos 11 x$ .

A) $f(x) =\cos 8 x \cos 3 x$
B) $f(x) =2 \cos 8 x \sin 3 x$
C) $f(x) =2 \cos 8 x \cos 3 x$
D) $f(x) =2 \cos 16 x \cos 6 x$