The function $f(x)=\cot x$ is discontinuous on the set

Question

\begin{array}{1 1}(A)\;\left \{x=n\pi:n\in z\right \} & (B)\;\left \{x=2n\pi:n\in z\right \}\\(C)\;\left \{x=(2n+1)\frac{\pi}{2};n\in z\right \} & (D)\;\left \{x=\frac{n\pi}{2};n\in z\right \}\end{array}