Let $\; f:R \rightarrow R$ be given as $\;f(x)=\tan x $. Then $\;f^{-1}(1)$ is

Question

\begin{array}{1 1}(A)\;\frac{\pi}{4} & (B)\;{n\pi+\frac{\pi}{4}:n\in Z}\\(C)\;does\;not\;exist & (D)\;none\; of\; these\end{array}