Giải hệ phương trình x-y = pi/3 và cosx = cosy = -1

A. $\left\{\begin{array}{l}x=\frac{\pi }{6}+k2\pi \\ y=-\frac{\pi }{6}+k2\pi \end{array}\right.(k\in Z)$

B. $\left\{\begin{array}{l}x=\frac{2\pi }{3}+k2\pi \\ y=\frac{\pi }{3}-k2\pi \end{array}\right.(k\in Z)$

C. $\left\{\begin{array}{l}x=\frac{2\pi }{3}+k2\pi \\ y=\frac{\pi }{3}+k2\pi \end{array}\right.(k\in Z)$

D. $\left\{\begin{array}{l}y=\frac{\pi }{2}+k2\pi \\ y=\frac{\pi }{6}+k2\pi \end{array}\right.(k\in Z)$