9) For this question, assume that expectations of the price level and productivity are accurate. For this economy, we know that the natural rate of unemployment should depend on which of the following? A) the level of productivity, but not its rate of growth B) the rate of growth of productivity, but not its level C) neither the level of productivity nor its rate of growth D) the level of productivity, its rate of growth, and the history of its recent change E) both the level of productivity and its rate of growth