虚拟语气倒装
当虚拟条件句中含有were，had，should，could等动词时，可以将if省略，然后将were，had，should，could 等词移至句首：
1）If he should fail，he would kill himself.
→Should he fail，he would kill himself.
万一失败，他就会自杀。
2）If I were you，I would do it at once.
→Were I you，I would do it at once.
假若我是你，我就会马上做。
3）If I could do it，I would.
→Could I do it，I would.
要是我能做此事，我一定会做。
4）If he had seen you yesterday，he would have asked you about it.
→Had he seen you yesterday，he would have asked you about it.
他昨天要是看到了你，他就会问你这事了。
再看一些例句：
1）Were they here now, they could help us.
=If they were here now, they could help us.
他们现在在的话，就会帮助我们了。
2）Had you come earlier, you would have met him.
=If you had come earlier, you would have met him.
你来得早一点，就碰到他了。
3）Should it rain, the crops would be saved.
=Were it to rain, the crops would be saved.
假如下雨，庄稼就有救了。
4）Were I（= If I were）in your place，I wouldn’t do it．
5）Had you（= If you had）seen it，you would have believed．
6）Were they to get married（= If they were to get married），the would not be happy．
7）Should he come，tell him to ring me up.
他要是来了，让他给我打个电话。
8）Were I in your position，I would go.
如果我处于你的地位，我就去。
9）Had they not helped us，our experiment would have failed.
如果没有他们的帮助，我们的试验是会失败的。
典型例题：
1）Not until the early years of the 19th century___ what heat is
A. man did know
B. man knew
C. didn\'t man know
D. did man know
答案为D.否定词Not在句首，要求用部分倒装的句子结构。
2）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 realize
答案为B。
3）Do you know Tom bought a new car?
I don\'t know, ___.
A. nor don\'t I care
B. nor do I care
C. I don\'t care neither
D. I don\'t care also
答案为B. 句中的nor引出部分倒装结构，表示\"也不\"。由so, neither, nor引导的倒装句，表示前一情况的重复出现。其中, so用于肯定句, 而neither, nor 用在否定句中。
4）_____ to do the work, I should do it some other day.
A. If were I
B. I were
C. Were I
D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词，通常将if省略，主语提前, 变成were, should, had +主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说Were I not to do, 而不能说Weren't I to do。
5）__________ your address，I would have written to you.
A. Did I know
B. Were I to know
C. Had I known
D. If I should know
此题应选C。这是虚拟语气的倒装形式。
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