In the adjacent figure, x-axis has been taken down the inclined plane. The coefficient of friction varies with `x` as `mu = kx`, where `k = tan theta`. A block is released at O
Frictional force acting on the block after it comes to rest :
A. `mg sin theta`
B. `2mg sin theta`
C. `(mg sin theta)/(2)`
D. `2 mg cos theta`