If $A+B+C=\pi$ then $\cos^2A+\cos^2B+\cos^2C$ is equal to

Question

$\begin{array}{1 1}(a)\;1-\cos A\cos B\cos C&(b)\;1-2\sin A\sin B\sin C\\(c)\;1-\sin A\sin B\sin C&(d)\;1-2\cos A\cos B\cos C\end{array}$