on earth 到底
【講解】
這條成語常與代詞who和what、關系副詞 when,where, why,how等連用,表示強調,相當于后綴-ever。
【對話】
A:Why did you stand there without a word?
A:你怎么站那兒一句話也沒有?
B:I didn't know what on earth to answer.
B:我不知到底該說些什么。
A:Then, why did you say sorry to the teacher?
A:那你怎么不和老師說你抱歉?
B:I don't know, I just felt afraid at that time.
B:我也不清楚自己是怎么回事,那會兒我就是覺得害怕。
A:You should change it.
A:你該把這一點改掉。