A solid sphere of uniform density and radius R applies a gravitational force of attraction equal to F_{1} on a particle placed at P, distance 2R from the centre O of the sphere. A spherical cavity of radius R/2 is now made in the sphere as shown in figure. The sphere with cavity now applies a gravitational force F_{2} on same particle placed at P. The ratio F_{2}/F_{1} will be

(a) 1/2

(b) 7/9

(c) 3

(d) 7