She on her homework in her study now . A. must workB. can workC. must have workedD. must

问题补充：

She on her homework in her study now .

A. must work

B. can work

C. must have worked

D. must be working

答案：

A. must work

B. can work

C. must have worked

(答案→)D. must be working

解析：对正在发生的事进行推测。