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.