改写句子。 1. They did not go to the Summer Palace because they had a lot of work to do. 2. When he heard a cry for help, he rushed out. 3. Because he recognized the man who had been his classmate ten years before, he was happy. 4. When the students went home from school, they talked and laughed. 5. As he was very old, he had to give up his teaching. 6. As he was an engineer, he knew exactly what to do. 7. The children went out to play after they had finished their homework. 8. As she had been given such a good chance, how could she let it slip away? 9. When he passed by the house, he saw a girl playing the piano. 10. As he had not found the wallet, he had to borrow some money from her.