Last Tuesday, Mr. Chen was reading a book in his office after school. To his surprise, a ball flew in suddenly and hit him on the head. He took the ball to the window, but he only saw a group of boy students running away quickly and theydisappearedin a minute. He sat down again and went on with his reading.

    After about two hours, it got dark. Mr. Chen decided to leave for home. Looking at the ball, he wanted to know what to do with it. He knew the owner（主人） of the ball must want to get it back. He got out of his office and walked to the playground. He put the ball at the center of the playground with a piece of paper on it. He wrote on the paper, "Be careful next time, my boy!" Then he walked away.

    The next morning, when Mr. Chen opened his office, he found the same piece of paper on the floor. Some words were behind it, "Thank you for your kindness （好意）, sir. You are a great man."