509.Has Ingrid handed in her paper yet?
I'm not sure.She _____ on it last week.
A.was working
B.has worked
C.worked
D.had worked
510.Where were you at lunch time?I _______ a seat for you in the dining hall.
A.saved
B.was saving
C.have saved
D.had saved
509.答案是A;由I'm not sure得知，上周在写，是否写好不清楚；而C则表示上周写完了。
510.答案是B;此题save动作发生在吃午饭的时候。
