The first question. The question that started this whole mess. The question The Fourth Doctor never actually answered, but just simply left be:
"Do I have the right?"
That question allowed the Daleks to survive, and his presence altered Davros of the existence of the Timelords, which began their plotting against them, which led to the last great Time War, which pitted two powerful races against each other, only to sear them both away from all existence. Mostly.
At the fall of the Eleventh, that question will be asked once more, and the subjects of the Silence, who treat the Doctor like a God, will see their Lord fall, and their faith shattered, as his last words answer the question:
The Master said that the Valeyard was somewhere between the 12th and his final regenerations. A sort of impossibility at the time, but now? Now it's could well be.