A level improvement

Is it possible to get three A for final exam A level ,by working hard remain 4 months(from D to A )?

Yeah. I think its possible, it will be hard since you're coming from a D to an A, but it's possible. You have to revise very hard for it like your life depends on it (it probably does if you're in Y13 and going to uni next year). You need to make sure to do so many practice papers in times conditions and revise quite a lot to ensure that you're on top of all your subjects. I would recommend looking over your past tests and revise the areas you struggled on and revise those first, then work backwards from the hardest topic to the easiest. And do a lot of practice questions and papers. It will be hard, but its possible.