not … until … 句型的强调句
A. 句型为：It is/ was not until + 被强调部分 + that + 其他部分
普通句：He didn't go to bed until/ till his wife came back.
强调句：It was not until his wife came back that he went to bed.
注意：此句型只用until，不用till。但如果不是强调句型，till, until可通用;因为句型中It is/ was not ... 已经是否定句了，that后面的从句要用肯定句，切勿再用否定句了。
有这样一道考题，其中涉及了 not…until… 句型：
It was not __________ he took off his dark glasses __________ I realized he was a famous singer.
A. when，that B. until，that C. until，when D. when，then
此题选 B。考查 not...until 的强调结构，其基本句型为：
It is (was) not until (时间状语) that (不用否定)
他妻子走了之后他才来。
正：He didn’t come until his wife left.
正：It was not until his wife left that he came.
直到雨停他们才出发。
正：They didn’t start until the rain stopped.
正：It was not until the rain stopped that they started.
另外以下问题特别值得注意：
1.注意不用强调句型时,如用not until开头,用主谓倒装，如：
She didn't remember her appointment with the doctor until yesterday.
It was not until yesterday that she remembered her appointment with the doctor.
Not until yesterday did she remember her appointment with the doctor.
2. 涉及强调句式“用It is还是用It was”的问题。这与not...until...句型没有直接的联系。
我们可以根据原句时态，来确定用It is还是用It was。如果原句时态属于现在时间范畴（包括一般现在时，现在进行式，现在完成时，一般将来时等），则用It is …；如果原句时态属于过去时间范畴（包括一般过去时，过去进行时，过去完成时，过去将来时等），则用It was … 例如：
It is at ten o’clock that the meeting will take place.
What is it that you want me to do now?
It was not until yesterday that I heard the news.
Was it John that broke the window this morning?
其实，not...until...句子用一般现在时或将来时并不鲜见。例如：
You won’t succeed until you try three times.
It is not until you try three times that you will succeed.
此外，情态动词还可用于It be中：
It might have been John that bought a new book for Mary yesterday.
It may be next week that she leaves for Tokyo.
It mast have been a thief that broke in the house.
It can’t be Tom that has damaged the desk.
It will not be you that will have to take the blame for this.
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