$A$ car moves along a circular track of radius $R$ banked at an angle of $30^o$ to the horizontal. The coefficient of static friction between the wheels and the track is $\mu$. The maximum speed with which the car can move without skidding out is

• A
  ${[gR(\mu + \tan \theta) / (1 - \mu \tan \theta)]}^{1/2}$
• B
  ${[gR(1 - \mu \tan \theta) / (\mu + \tan \theta)]}^{1/2}$
• C
  ${[gR(\mu + \sqrt{3}) / (1 - \mu \sqrt{3})]}^{1/2}$
• D
  None