A、He put it back on the ground. B、He put it into his own pocket. C、He threw it into the trash can. D、He gave it to the police. D

When I was walking down the street the other day, I happened to notice a small brown leather wallet lying on the sidewalk. I picked it up and opened it to see if I could find out the owner’ s name. There was nothing inside it except some change and an old photograph—a picture of a woman and a young girl about twelve years old, who looked like the woman ’ s daughter. I put the photograph back and took the wallet to the police station.
    That evening I went to have dinner with my aunt and uncle. They had also invited a young woman so that there would be four people at the table. Her face seemed familiar. I was quite sure that we had met before, but I couldn’ t remember where I had seen her. In the course of conversation, however, the young woman happened to mention that she had lost her wallet that afternoon. All at once I realized where I had seen her. She was the young girl in the photograph, although she was now much older. She was very surprised, of course, when I was able to describe her wallet to her. Then I explained that I had recognized her from the photograph I had found in the wallet. My uncle insisted on going to the police station immediately to claim the wallet. As the police sergeant handed it over, he said that it was amazing that I had not only found the wallet, but also the person who had lost it.
Q:
16. Why did the speaker open the wallet?
17. What did the speaker do with the wallet?
18. When did the speaker find the owner of the wallet?