(2)对以must提出的疑问句，如作否定回答时，要用needn‘t或用don’t (doesn‘t) have to (不 必)来回答，而不用mustn’t，因为mustn‘t表示的是“禁止”或“不许可”之意，如： ---- Must we finish the work tomorrow? ---- No, you needn't (don't have to), but you must finish   it in three days.