The upper half of a inclined plane of inclination $$\theta$$ is perfectly smooth while lower half is rough .A blocl starting from the rest top of the plane will gain come to rest at the bottom ,if the coefficients of the friction betwwen the block and lower half of the plane is given by:

A

$$\mu=\tan \theta$$

B

$$\mu=\frac{1}{\tan \theta}$$

C

$$\mu=\frac{2}{\tan \theta}$$

D

$$\mu=2 \tan \theta$$