The displacement of a S.H.O. is given by the equation $\mathrm{x}=\mathrm{A}$ $\cos \{\omega t+(\pi / 8)\}$. At what time will it attain maximum velocity?
(A) $(3 \pi / 8 \omega)$
(B) $(8 \pi / 3 \omega)$
(C) $(3 \pi / 16 \omega)$
(D) $(\pi / 16 \pi)$.