The first pulley, tension F 1= 12(G+G movement) = 12(G+G)=G,
Second pulley, tension F2= 12(F 1+G moving) = 12(G+G)=G,
The third pulley, tension F3= 12(F2+G moving) = 12(G+G)G,
…
The nth pulley, the pulling force Fn= 12(Fn- 1+G moving) = 12(G++G)=G,
When the pulley block is balanced, the pulling force is F. When a moving pulley with the same mass is added, when the pulley block is balanced again, the pulling force is still F.
So choose B.