A sphere of radius r is kept on a concave mirror of radius of curation `R`. The arrangement is kept on a horizontal surface (the surface of concave mirror is friction less and sliding not rolling). If the sphere is displaced from its equilibrium position and left, then it executes `S.h.M.` The period of oscillation will be
A. `2pisqrt((((R-r)1.4)/(g)))`
B. `2pisqrt(((R-r)/(g)))`
C. `2pisqrt(((rR)/(a)))`
D. `2pisqrt(((R)/(gr)))`
