当主句是否定句时,它引出的意思是"直到（某时）（某动作）才（发生）" ,这时候常会出现"not until …"的结构,如果将 "not until …"的结构放在句首,那么主句要写成倒装句.例如：
He didn't go to sleep until 12 last night .
他昨晚直到十二点钟才睡觉.
They didn't realize their fault utill we pointed it out to them .
直到我们向他们指出了他们的错误,他们才意识到.
Not until we pointed out their fault to them did they realize it .
直到我们向他们指出了他们的错误,他们才意识到