I see in an exercise "Я делаю упражнениa на разные правила" (вини.). In the Dictionary I find "упражнение по испанском языке, в рояле" (пред.). The difference between "practice the piano" (playing scales up and down) and "practice in the piano "( playing Klavier Konzert KW-120, for instance), or "practice in the car" (not starting it) or "practice the car" (running through the streets) is clear. Perhaps is this the difference? I see no other else. Thanks