If $f(x)=\sec 2 x+\operatorname{cosec} 2 x$, then $f(x)$ is discontinuous at all points in
(a) $\{n \pi, n \in N\}$
(b) $\left\{(2 n \pm 1) \frac{\pi}{4}, n \in I\right\}$
(c) $\left\{\frac{n \pi}{4}, n \in I\right\}$
(d) $\left\{(2 n \pm 1) \frac{\pi}{8}, n \in I\right\}$