A, aluminum ring in the process of falling, through the change of magnetic flux, induced current, so a is wrong;

B. When the magnetic flux of the aluminum ring changes, an induced current is generated, and an ampere resistance is generated, so that the pressure of the magnet on the desktop is greater than gravity. When there is no magnetic flux change in the middle of the bar magnet, there is no ampere force when there is no induced current, so the pressure on the table is equal to gravity, so B is wrong;

C. When the magnetic flux of the aluminum ring changes and induces current, the ampere force always hinders the relative motion, so the ampere force is always upward, so c is wrong;

D, from option B, the acceleration is less than or equal to G, so D is correct;

So choose: D.