If $A = \begin{bmatrix} x & 0 \\ 1 & 1 \end{bmatrix}$ and $B = \begin{bmatrix} 4 & 0 \\ -1 & 1 \end{bmatrix}$, then value of $x$ for which $A^2 = B$ is : (A) $-2$ (B) $2$ (C) $2$ or $-2$ (D) $4$