The function $f(x)=\frac{x-\frac{\pi}{2}}{1-\left(x-\frac{\pi}{2}\right) \cot x}$ in $(0, \pi)$ has
(a) one maximum in $\left(0, \frac{\pi}{2}\right)$ and one minimum in $\left(\frac{\pi}{2}, \pi\right)$
(b) one minimum in $\left(0, \frac{\pi}{2}\right)$ and one maximum in $\left(\frac{\pi}{2}, \pi\right)$
(c) both maximum and minimum in $\left(0, \frac{\pi}{2}\right)$
(d) both maximum and minimum in $\left(\frac{\pi}{2}, \pi\right)$