A spiral galaxy can be approximated as an infinitesimally thin disk of a uniform surface mass density (mass per unit area) located at z = 0. Two stars A and B start from rest from heights 2z0 and z0 (z0 << radial extent of the disk), respectively, and fall towards the disk, cross over to the other side, and *** periodic oscillations. The ratio of time periods of A and B is
(A) 2–1/2
(B) 2
(C) 1
(D) 21/2
