A. Since the pulling force F is in the same direction as the speed v, the instantaneous power of the pulling force is P=Fv, so A is wrong;
B. The system is initially at rest, and the spring force is equal to The component force of A's gravity along the slope. When B just leaves C, the elastic force of the spring is equal to the component force of B's ??gravity along the slope, so m2gsinθ=kx2. However, since the spring is compressed at the beginning, d>x2 , so m2gsinθ C. When B just leaves C, for A, according to Newton’s second law: F-m1gsinθ-kx2=m1a1, when it starts again, A is balanced , then we have: m1gsinθ=kx1, and d=x1 The quantity is equal to the work of pulling force minus the increase in kinetic energy of the system and gravitational potential energy, which is: Fd-m1gdsinθ-12m1v2, so D is wrong. So choose: C.