7. Two identical conducting spheres are charged to +2 Q and -Q . respectively, and are separated by a distance d (much greater than the radii of the spheres) as shown above. The magnitude of the force of attraction on the left sphere is F1. After the two spheres are made to touch and then are re-separated by distance d, the magnitude of the force on the left sphere is F2. Which of the following relationships is correct?
(A) 2F1=F2
(B) F1=F2
(C) F1=2F2
(D) F1=8F2