1. He could repair the broken vase.
-> The broken vase could be repaired by him.
2. Although he had a good salary, he was unhappy in his job.
-> In spite of having a good salary, he was unhappy in his job.
3. "Would you like to come round for a drink?" he said.
-> He invited me to come round for a drink.
4. Would you like me to call the police?
-> If you wanted, i would call the police.