67. I didn't realize my mistake until I entered the office.
點(diǎn)睛
not...until句型使用廣泛，表示“（不）……直到”。其中，not可以省略。如：
Wait until tomorrow. 等到明天。
考點(diǎn)歸納
與not...until句型類似的是till，二者用法的區(qū)別比較微妙，需要特別注意：
當(dāng)主句是否定句時(shí)，意思是“直到（某時(shí)）（某動(dòng)作）才（發(fā)生）”，這時(shí)候常會(huì)使用not until的結(jié)構(gòu)；如果將not until結(jié)構(gòu)放在句首，那么主句要用倒裝形式。如：
1) He didn't go to sleep until 12 last night. 他昨晚直到12點(diǎn)鐘才睡覺。
2) Not until we pointed out their fault to them did they realize it. 直到我們指出他們的錯(cuò)誤，他們才意識(shí)到。
當(dāng)主句是肯定句時(shí)，意思是“直到（某時(shí)某動(dòng)作停止了）”，這時(shí)候常會(huì)使用till。如：
1) The students made much noise till the teacher came into the classroom. 直到老師走進(jìn)教室，學(xué)生們才停止了吵鬧。
2) Don't open it till your birthday. 等到你生日那天再打開。
另外，until可以放在句首，而till則不行。如：
1) Until they used up all their money, the young couple were very happy. (√)
2) Till they used up all their money, the young couple were very happy. (×)
