條件狀語從句，由if, as (so) long as和unless引導。
eg：You can arrive in Beijing earlier for the meeting provided you don't mind taking the night train.
If he had followed my advice,he would be quite all right now.（從句
If China had not been liberated,the working people would still be
leading a miserable life.（ 從句表示與過去的事實相反，主句說明與現在的
Were I (=If I were) in your place,I wouldn't give it up so early.
Had I (=if I had) known,I might have joined you in the discussion.
Should you (=If you should) be interested,I have a book on the subject
you might like.
were my sister！如果她是我的妹妹就好了！
It would be good to leave the matter in his charge.如果把這件事讓
該句可改寫成：It would be good if we could leave thematter in his
Doing the work in that way would have cost much more timeand money.
該句可改寫為：If we had done the work in that way,it wouldhave cost
much more time and money .
A man who is always thinking of others would not have donesuch a thing.
Anyone being his position would have made no reply.任何人處在他那
該句可改寫為：If anyone had been in his position he wouldhave made
A less complicated problem would have easily been solved.如果問題
該句可改寫為：If the problem had been less complicated,it would have
easily been solved.
We could have done better under more favourableconditions.
此句可改寫為：If the conditions had been more favourable, we could
have done better.
This change could not have taken place without a solid industrial
此句可改寫為：If it had been without a solid industrial
foundation,this change could not hav e taken place.
3.用but或but for引導含蓄條件句（but後跟從句，but for後跟短語）
But for your help,our experiment wouldn't have been sosuccessful.
But for the storm,we should have arrived earlier.
We would have invited them to the dance,but they were too busy.
此句可改寫為：If they had not been so busy,we would haveinvited them
to the dance.
But that he is in hospital,He would go abroad for hissummer vacation.
該句可改寫為：If he wereint in hospital,he would go abroadfor his