Let $\theta = \frac{2\pi}{7}$ and consider the following matrix
$$A = \left(\begin{array}{rr} \cos\theta & -\sin\theta \\ \sin\theta & \cos\theta \end{array}\right)$$
If $A^n$ means $A \times \cdots \times A$ ($n$ times), then $A^{100}$ is\\
(A) $\left(\begin{array}{rr} \cos 2\theta & -\sin 2\theta \\ \sin 2\theta & \cos 2\theta \end{array}\right)$\\
(B) $\left(\begin{array}{rr} \cos\theta & -\sin\theta \\ \sin\theta & \cos\theta \end{array}\right)$\\
(C) $\left(\begin{array}{ll} 1 & 0 \\ 0 & 1 \end{array}\right)$\\
(D) $\left(\begin{array}{rr} 0 & -1 \\ 1 & 0 \end{array}\right)$.