A ring having non-uniform distribution of mass `M` and radius `R` is being considered. A point mass `m_(0)` is taken slowly towards the ring. In doing so, work done by the external force against the gravitational force exerted by ring is
A. `(GMm_(0))/(sqrt(2)R)`
B. `(GMm_(0))/R[1/sqrt(2)-1/(sqrt(5))]`
C. `(GMm_(0))/R[1/sqrt(5)-1/(sqrt(2))]`
D. It is not possible to find the required work as the nature of distribution of mass is not known.