Express the following as the sum difference of cosines and sines $2\cos 7\theta.\cos 3\theta$

Question

$\begin{array}{1 1}(A)\;\cos 10\theta+\cos 7\theta\\(B)\;\cos 10\theta+\cos 4\theta\\(C)\;\cos 8\theta+\cos 7\theta\\(D)\;\text{None of these}\end{array} $