If the matrix $ \begin{bmatrix} -x & x & 2 \\ 2 & x & -x \\ x & -2 & -x \end{bmatrix} $ is non-singular, then value of `x` is -- (a) `-2\le\x\le2`, (b) Any real number except `\pm2`, (c) `x\ge2`, (d) `x\le-2`