"on earth" in Chinese (Simplified)
到底究竟 (语气加强)
Definition
用于强调疑问句，表达惊讶、困惑或难以置信，比如“这到底是什么？”这里不指地球本身，而是加强情感语气。
Usage Notes (Chinese (Simplified))
'On earth' 通常用于口语或书面英语，表达疑问时加强语气。多跟在疑问词后使用（如 'what', 'why', 'how' 等）。正式场合不建议使用。
Examples
What on earth is that noise?
那到底是什么声音？
How on earth did you do that?
你是**到底**怎么做到的？
Why on earth would you say that?
你**到底**为什么会那样说？
Where on earth have you been all day?
你**到底**一整天去哪了？
Who on earth would believe that story?
谁**到底**会相信那个故事？
When on earth are you going to clean your room?
你**到底**什么时候要打扫房间？