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1)　句首为否定或半否定的词语，如no, not, never, seldom, little, hardly, at no time, in no way, not until… 等。

Never have I seen such a performance.

Nowhere will you find the answer to this question.

Not until the child fell asleep did the mother leave the room.

当Not until引出主从复合句，主句倒装，从句不倒装。

注意： 如否定词不在句首不倒装。

I have never seen such a performance.

The mother didn't leave the room until the child fell asleep.

典型例题

1)　Why can't I smoke here?

At no time___ in the meeting-room

A. is smoking permitted　　B.　smoking is permitted

C. smoking is it permitted　D.　does smoking permit

答案A. 这是一个倒装问题。当否定词语置于句首以表示强调时，其句中的主谓须用倒装结构。 这些否定词包括no, little, hardly, seldom, never, not only, not until等。本题的正常语序是 Smoking is permitted in the meeting-room at no time.

2) Not until the early years of the 19th century ___ what heat is.