until的用法
until（或till）在句子中用作介詞或連詞，其含義和since有類似之處，只是since強調(diào)的是某一段的時間的起點（“從……”），而until表示的是一段時間的終點（“到……”）。
一．由until （或till）構成的介詞短語或引起的從句在句中作狀語時，如果是肯定句，句子的謂語動詞或主句中的謂語動詞一般是延續(xù)性的；在否定句或含有否定意義的句子中，句子的謂語動詞或主句中的謂語動詞，既可是非延續(xù)性的，也可以是延續(xù)性的。肯定句側重動作延續(xù)的時間，否定句說明動作開始的時間。
例如：
They thought their bodies would be well kept in these until they would come back to life.
He and the other doctors did not leave until the operation was over.
They are not going back to work until they get it.
He doesn’t sit down until the other person takes his seat.
And then they went on with their work at the empty loons until late into the night.
No more work was done on it until the People’s Republic of China was founded.
二．對含有“not … until …”結構的句子進行強調(diào)時，須用it is (was )not until…that…。
例如：
It was not until she took off her dark glasses that I realized she was a famous film star.
It was not until I saw Margaret the next morning, however, that I felt happy.
三．如果把“it is (was )… that ….”這個強調(diào)結構的框架去掉，句子就須用倒裝語序。若是一個復合句時，要倒裝主句中的主謂部分。
例如：
Not until the early years of the 19 th century ____ what heat is.
A. man did know B. man knew C. didn’t man know D. did man know
答案是 D
Not until I began to work _____ how much time I had wasted.
A. didn’t I realize B. did I realize C. I didn’t realize D. I realized
答案是B