— The light is still on in his room. Do you know ?— In order to practise for the English s

问题补充：

— The light is still on in his room. Do you know ?

— In order to practise for the English singing party.

A. if he works hard

B. who he is studying with

C. why he is so busy

D. when he will stop working

答案：

A. if he works hard

B. who he is studying with

(答案→)C. why he is so busy

D. when he will stop working

解析：if是否；who谁；why为什么；when什么时候。根据下文，为了这次英语歌唱晚会做练习。可知上文问的是原因，故选C，他房间的灯还在亮着，你知道他为什么这么忙吗？故选C。