( A ) $\sqrt{\frac{g}{R^2} \frac{\mu_s + \tan \theta }{1 - \mu_s \tan \theta}}$

( B ) $\sqrt{gR^2 \frac{\mu_s + \tan \theta }{1 - \mu_s \tan \theta}}$

( C ) $\sqrt{gR \frac{\mu_s + \tan \theta }{1 - \mu_s \tan \theta}}$

( D ) $\sqrt{\frac{g}{R} \frac{\mu_s + \tan \theta }{1 - \mu_s \tan \theta}}$