---Has Peter handed in his paper yet?

       ---I’m not sure．He _______ on it last week．

       A．was working                                B．has worked         

       C．worked                                      D．had worked

---Has Peter handed in his paper yet?

       ---I’m not sure．He _______ on it last week．

       A．was working          B．has worked         

       C．worked                 D．had worked

 ---Has Peter handed in his paper yet?

       ---I’m not sure．He _______ on it last week．

       A．was working                               B．has worked         

       C．worked                                      D．had worked

--Has Peter handed in his paper yet?
---I’m not sure. He _______ on it last week.