The inversion of subject and auxiliary verb takes place if one of the following adverbs or adverbial phrases
introduces the sentence:
hardly (ever), never, seldom, never before, little, under no circumstances, by no means, only, rarely, scarcely,
no sooner..than, hardly..than, at no time, neither, so, in no case, on no account, nowhere etc.
Rewrite the sentences starting with the words in italics or those in brackets:
1.He seldom appeared before 10.
2. She had no sooner come home than she began to help her mother.
3. They only then realized what they had done.
4. People do not think of using their cars less until prices of petrol go up.(Use 'not until')
5. People feel rarely prepared to give up their cars in order to help the environment.
6. I have never been in such a terrible traffic-jam in all my life.
7. As soon as we had parked the car, we saw policeman approaching us.(Use 'no sooner..than')
8. He seldom kept his promises.
9. I will not agree to your to your plan of travelling to Africa under any circumstances.
10. You have not taken any risks at any time.
11. The plane took off only after a few minutes of delay.
12. There had never been demonstrations like that before.