In the given figure, the sphere rolls without slipping on the plank which is moving with constant velocity $v_{0}$ - The radius and angular velocity of the sphere is $r$ and $\omega$ respectively. The velocity of centre of mass of the sphere is:
(a) $v_{0}+r \omega$
(b) $v_{0}-r \omega$
(c) $r \omega$
(d) $v_{0}$