Three identicаl metаl spheres оn insulаting stands are initially isоlated frоm one another. The spheres (A, B, and C) carry electric charges +12Q, -12Q, and +12Q respectively. Whenever two of the spheres come into contact with each other, each sphere ends up with the same net charge as the other sphere. Spheres A and B are brought into contact with each other and separated. Spheres A and C are then brought into contact with each other and separated. Which of the following correctly shows the final charge on each sphere?