—Has Tom finished his task yet?—I’m not sure. But he on it last weekA. was workingB. has

问题补充：

—Has Tom finished his task yet?

—I’m not sure. But he on it last week

A. was working

B. has been working

C. worked

D. had been working

答案：

(答案→)A. was working

B. has been working

C. worked

D. had been working

解析：考查时态。句意：——Tom完成了他的任务吗？——我不确定。但是他上周一直致力于这个任务。根据语境，说明与过去有关，且表示过去一段时间（last week）内一直在做某事，故使用过去进行时。