A solid cylinder is rolling without slipping down an inclinc of inclination $\theta$. Minimum coc[ficicnt of friction so that the cylinder docs not slip on the incline is
(a) $\tan \theta$
(b) $\frac{\operatorname{lan} \theta}{2}$
(c) $\frac{\tan \theta}{3}$
(d) $\tan \left(\frac{\theta}{3}\right)$