用所给词的适当形式填空 1. We're doctors, so it's our _______ (duty) to save patients. 2. The road is _______ (crowd). Mr. Wang drives his car slowly. 3. What causes the _______ (ill)? 4. Did they enjoy _______ (they) in the party yesterday? 5. —Where is your mother, Beibei? —She is busy _______ (answer) the telephone.