67.I didnt realize my mistake until I entered the office.
六级词汇讲解:
not...until句型使用广泛，表示一直到。其中，not可以省略。如:
Wait until tomorrow.等到明天。
英语六级考点归纳
与not...until句型类似的是till，二者用法的区别比较微妙，需要特别注意：
当主句是否定句时，意思是直到才，这时候常会使用not until的结构;如果将not until结构放在句首，那么主句要用倒装形式。如:
I ) He didnt go to sleep until 12 last night.
他昨晚直到12点钟才睡觉。
2 ) Not until we pointed out their fault to them did they realize it.
直到我们指出他们的错误，他们才意识到。
当主句是肯定句时，意思是直到，这时候常会使用till。如:
1) The students made much noise till the teacher came into the classroom.
直到老师走进教室，学生们才停止了吵闹。
2 ) Dont open it till your birthday.
等到你生日那天再打开。
另外，until可以放在句首，而till则不行。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.