Two concentric shells of mass `m_(1)` and `m_(2)` are situated as shown. Find the force on a particle of mass `m` when the particles is located at `(a) r=r_(1),(b)r=r_(2),(c)r=r_(3)`. The distance `r` is measured from the centre of the shell.

Options

A. `(GM_(1)m)/(b^(2))`
B. `(GM_(2)m)/(b^(2))`
C. `G((M_(1) + M_(2))m)/(b^(2))`
D. `G((M_(1) - M_(2))m)/(b^(2))`