I just took another look at this poll. As RYou pointed out, the wording of the question allowed more than one correct answer. To avoid that, the question could have been, What will cause Trump's presidency to end? It's true he got impeached (twice), but getting impeached didn't cause his presidency to end. However, would that question ensure the correct answer could always be determined? Yes, but only if the exact moment during the new president's inauguration could be known at which Trump's presidency ended. If Trump died ten minutes before that moment, the vice-president would take over for ten minutes and "He dies in office" would be correct. If Trump died at that exact moment, I would rule that serving four years rather than dying was the cause of his presidency ending, but others might argue that both were correct.