\[\begin{array}{1 1}(A)\;f \;is\;everywhere\;differentiable\\(B)\;f \;is\;everywhere\;continuous\;but\;not\;differentiable\;at\;x=n\pi,n\in z \\(C)\;f\;is\;everywhere\;continuous\;but\;not\;differentiable\;at\;x=(2n+1)\frac{\pi}{2},n\in z\\(D)\;none\;of\;these\end{array} \]
