The normal order of words in a sentence is subject, verb and object. But sometimes certain adverbs are put first and then this order is inverted, and the verb comes before the subject.

Hardly had I reached the station when the train arrived.
Scarcely had the game started when the rain came pouring down.

No sooner had she read the telegram than she fell down fainting.
Never before had I seen such a vast crowd.

Adverb particles (e.g. up, down, in, out, on, off, away and back) can also come before the subject. The inversion is for the sake of emphasis.

Off they went on a hunting trip. (Inverted word order)
They went off on a hunting trip. (Normal word order)
Down he fell from his horse, with a heavy thud.

Rewrite the following sentences, putting the adverb first and inverting the subject and verb.

1. I have seldom heard such a beautiful voice.

2. He had hardly finished his lunch when someone knocked at the door.

3. I have never heard such utter nonsense.

4. I had hardly arrived when trouble started.

5. I was able to appreciate her only after her death.

Answers

1. Seldom have I heard such a beautiful voice.

2. Hardly had he finished his lunch when someone knocked at the door.

3. Never have I heard such utter nonsense.

4. Hardly had I arrived when trouble started.

5. Only after her death was I able to appreciate her.