---The light in the room is still on. Do you know?---In order to prepare for the coming ex

问题补充：

---The light in the room is still on. Do you know?

---In order to prepare for the coming exam.

A. if he works hard

B. why he stays up late

C. why is he so busy

D. when he will stop working

答案：

A. if he works hard

(答案→)B. why he stays up late

C. why is he so busy

D. when he will stop working

解析：根据题干，我们可知本句是一个宾语从句或间接引语。宾语从句或间接引语的语序应该用陈述句语序，通过观察发现应排除C；根据答语“为了将来的考试做准备。”可知，上句应该是问原因的，故用why。所以本题选B。