Mr. Green and his wife had a dog. When they went out, they always left the dog inside the house. One evening they wanted to go to the cinema, so they left the dog in the house and locked the door and their garden gate. They went off in their car. When the film was finished, they went home. They opened the gate and put the car away. When they came to the front door, they found that the glass in the door was broken. The door was not locked and it was open. A robber! They went in and quickly looked in all the rooms to see if the robber had taken their things. However, everything was in the right place and nothing at all was missing. The dog was sleeping in the sitting-room. The wife was angry with the dog."Why didn't you guard the house?"she said. The dog was pleased to see Mr. and Mrs. Green. It began to wag its tail and then it went to a comer of the room and picked up something in its mouth. It went to the wife and dropped the thing at her feet. When she went to pick it up, she was very surprised. Can you guess what the dog's present was ?It was a man's finger! The end of the story is this. Mr. Green telephoned the police and told them everything. Three days later the police caught the robber. They found him easily. The robber was caught easily because   _  .
the police knew him the police happened to meet him Mr. Green know where he lived he had one of his fingers