Two trains A and B are running in the same direction on parallel tracks such that A is faster than B. If packets of equal weight are exchanged between the two, then

• A. A will be retarded but B will be accelerated
• B. A will be accelerated but B will be retarded
• C. there will be no change in velocity of A but B will be accelerated
• D. there will be no change in velocity of B, but A will be accelerated