The upper half of an inclined plane of inclination `theta` is perfectly smooth while lower half is rough . A block starting from rest at the top of the plane will again comes to rest at the bottom , if the coefficient of friction between the block and lower hald of the plane is given by

Options

A. `mu=(2)/(tan theta)`
B. `mu=2tan theta`
C. `mu=tan theta`
D. `mu=(1)/(tan theta)`