1. The letter written by him was very long. 2. We are interested in the goods produced by this factory. 3. She didn’t understand the word said by him. 4. He didn’t see the things kept in her box. 5. I don’t like the video bought yesterday. 6. This is the house built many years ago. 7. The question put to the professor was important. 8. When offered to work abroad, he refused. 9. The article on agriculture published in this magazine was written by Smith. 10. You can get the book recommended by our teacher in the library. 11. When used for building purposes, concrete is very important. 12. When completed, the new building will accommodate 3000 students.

Перефразирую все примеры, заменяя причастные обороты и безличные конструкции на обычные придаточные предложения (relative/temporal clauses):

1. The letter that he wrote was very long.

2. We are interested in the goods that this factory produces.

3. She didn’t understand the word that he said.

4. He didn’t see the things that were kept in her box.

5. I don’t like the video that was bought yesterday.

6. This is the house that was built many years ago.

7. The question that was put to the professor was important.

8. When he was offered work abroad, he refused.

9. The article on agriculture that was published in this magazine was written by Smith.

10. You can get the book that was recommended by our teacher in the library.

11. When it is used for building purposes, concrete is very important.

12. When it is completed, the new building will accommodate 3000 students.