1. When he returned to thank the doctor, he had already walked away.
2. When I went down to Tom's room he was sitting at his table reading a small book.
3. By the end of the last term we had learned many new words.
4. He called to his office as he had reached his house.
5. After they were drinking coffeee Meg invited him to go over the house.
6. By the time the police arrived, the robbers had already escaped.