A reflecting will have a mirror on the bottom where the light will bounce off a retracting uses lenses that focus the light
Marbles would have the greater density. Marbles would have the greater density because the molecules inside are more tightly packed. Even though sand has the greater mass it does not have the greater density. The sand doesn't have the greater density because it could be crushed in an instant, showing that if molecules are packed together tightly they will be tougher to break. The dice, I believe, still have a greater density than the sand.
C.ccccccccccccccccccccccccccccccccccccc