Paraphrase the sentences using Participle I.
1. After they had repaired the car, they drove on, though it was past midnight.
2. When I packed all my things, I still had enough time to write a few letters.
3. They were old friends, they had been at school together.
4. For an hour or so he watched a lovely film that he knew by heart, as he had seen it at least ten times.
5. When he was told that he would go there by plane, he felt excited, as he had never travelled by air before.
6. When we had reached the top of the mountain, we sank to the ground, too tired to do anything.
7. After he had worked at the Institute for five years, he decided to take a postgraduate course.
8. The experiment which is being made in our laboratory will be very important for our future work.
9. The letter was written in pencil, it was difficult to read.
10. They looked at the house which was being built on the other side of the river.
11. As he was not allowed to read, he most¬ly spent his time listening to the radio.
12. He asked for additional explanation as he was not satisfied with the answer.