第67句：

I didn't realize my mistake until I entered the office.

六級詞匯講解:
not...until句型使用廣泛，表示“(不)·一直到”。其中，not可以省略。如:
Wait until tomorrow.等到明天。

六級考點歸納：
與not...until句型類似的是till，二者用法的區別比較微妙，需要特別注意：

當主句是否定句時，意思是“直到(某時)(某動作)才(發生)”，這時候常會使用not until的結構;如果將not until結構放在句首，那么主句要用倒裝形式。如:
I ) He didn't go to sleep until 12 last night.
他昨晚直到12點鐘才睡覺。
2 ) Not until we pointed out their fault to them did they realize it.
直到我們指出他們的錯誤，他們才意識到。

當主句是肯定句時，意思是“直到(某時某動作停止了)”，這時候常會使用till。如:
1) The students made much noise till the teacher came into the classroom.
直到老師走進教室，學生們才停止了吵鬧。
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 ail their money, the young couple were very happy.(√)
2)Till they used up all their money, the young couple were very happy.(×)