Sally was a student. It was going to be her mother's birthday. She wanted to buy her a present that would be nice and useful but not expensive. A week before her mother's birthday, she went shopping after a quick and simple lunch. When she had been looking for half an hour, she found a shop that was selling cheep umbrellas , and decided to take a black one, since her mother had lost hers the month before. She thought, "You could carry that when you are wearing clothes of any color." So she decided to buy a lovely black umbrella and took it back to school with her until her classes had finished. On her way back home in the train that evening, she felt hungry because she had such a small lunch that she went along to the buffet car  for another sandwich and cup of coffee. She had left the black umbrella above her seat in the compartment , but when she got back, it had gone! When she had left the compartment, there had been no other passengers  in it, but now there were three. Sally began to cry when she saw that the umbrella was no longer there. The other passengers felt very sorry for her and asked what the matter was. She told them that the black umbrella she had bought for her mother was gone, and that she had to get out at the next station. After the three other passengers heard it, they asked her for her mother's address so that they could sent the umbrella to her if someone had taken it by mistake and brought it back after Sally had got out of the train. The next week, Sally heard from her mother. It said, "Thank you very much for your lovely presents, but why did you send me three black umbrellas?" What does the story infer ?
Her mother would write to her if she didn't receive the presents. The three umbrella were sent by the girl. Only four people had ever been to the compartment. Nobody brought the umbrella back.