从下列各题所给的A、B、C、D四个选项中选出可以填入空白处的最佳选项。
(   )1. Miss Li taught _______ Chinese last year.
      A. we    B. us   C. our D. ours
(   )2. —Is this your aunt’s car?
         —No, it isn’t. _______ is under the tree.
      A. Her    B. Him  C. Hers D. His
(   )3. —Must we get there at six tomorrow morning?
         —Yes, you must. _______ you’ll miss the early bus.
      A. Or     B. And   C. But   D. If
(   )4. —Could you tell us _______ you are buying the flowers for?
         —For my mother. It’s Mother’s Day today.
      A. when    B. where  C. how  D. who