A particle at rest is attracted towards a centre of force according to the relation =-mk° /x'. (here, m is the mass, x is the position from the center of force

A particle at rest is attracted towards a centre of force according to the relation =-mk° /x'. (Here, m is the mass, x is the position from the center of force and k is a constant of proportionality). The time required for the particle to reach the force centre from a distance d is (A) d/k (B) dm/k (C) d/mk (D) d/k