The set of critical points of the function $f(x)=x-\log x+\int_{2}^{\pi}(1 / z-2-2 \cos 4 z) d z$ is
(A) $\left\{\frac{\pi}{6}, \frac{n \pi}{2}+\frac{\pi}{6}\right\}, n \in N$
(B) $\{n \pi\}, n \in N$
(C) $\left\{\frac{\pi}{2}, \mathrm{n} \pi+\frac{\pi}{6}\right\}, \mathrm{n} \in \mathrm{N}$
(D) None of these