The static state of rod B shows that the forces on rod B are balanced, that is, the components of Ampere force and gravity are balanced along the inclined plane, and rod A moves upward at a uniform speed, which shows that the three forces of rod A are balanced, while rod C falls at a uniform speed, so that the gravity on rod C is balanced with the tension on the rope. From the B balance, we can see that the ampere force is F =mgsinθ, and from the A balance, we can see that F-bar is MGS in F = F+θ.

A, because the tension in the rope is equal, 2mgsinθ=mcg, that is, the mass of block C is 2msinθ, so A is correct;

Before B and B were put on, according to the conservation of energy, it is known that the increase of gravitational potential energy of A is also due to the decrease of gravitational potential energy of C, so B is wrong;

C and A are rising at a constant speed, and the gravitational potential energy is increasing, so we know that C is wrong according to the conservation of energy.

D, according to the balance of B-bar, F-an =mgsinθ, F-an = BIL ∴ I = MGsinθ BL, so d is correct;

So choose ad.