The bell rang and the class was over. The classroom became noisy. Some students went out of the classroom. I was just chatting with some of my classmates when Li Hong came to me. She smiled and said to me, "What's four minus four? Do you know?" "It's zero. That is easy." answered I. But Li Hong shook her head and said "It's wrong. It's eight." "Why? That's impossible!" "You will understand if you cut down four corners of a desk." said Li Hong. "Is that a joke?" "Oh, yes." We all laughed. During the class break, we had a good rest. We often have a pleasant break.