$\begin{array}{1 1}(A)\;n\pi+(-1)^n \large\frac{\pi}{2}&(B)\;2n\pi+(-1)^n \large\frac{\pi}{4}\\(C)\;n\pi+(-1)^n \large\frac{\pi}{6}&(D)\;2n\pi+ \large\frac{3\pi}{4}\end{array} $
