Lisa now stop for a short break. You should know that youall the morning.A. are workingB

问题补充：

Lisa, now stop for a short break. You should know that youall the morning.

A. are working

B. had been working

C. have been working

D. have worked

答案：

A. are working

B. had been working

(答案→)C. have been working

D. have worked

解析：考查动词时态。根据now stop for a short break，可知现在还在工作，再根据all the morning，可知整个早晨一直在工作，所以要用现在完成进行时态，表示从过去开始到现在一直在进行的动作。有可能还会进行下去。所以选C。