- did he stay up late last night? - Because he studied for the English exam. A. WhenB. Why

问题补充：

- did he stay up late last night?

- Because he studied for the English exam.

A. WhenB. Why C. Where

答案：

解析：考查情景交际。根据答语中的because可知，问句问的是“他昨晚为什么熬到很晚。”问原因用why。故选B。