​The Same Father   

　　Billy and his brother David are twins. They are 12 years old. They are in the same class. One day, the teacher assigned them to write a composition “My Mother”. David wrote one and Billy just copied it. On the next day, the teacher asked Billy, “How is it that your composition is exactly the same with David’s?” “We have the same mother, don’t we? ” Replied Billy. But the teacher asked Billy to rewrite the composition.
　　One week later, the teacher asked them to write a composition “My Father”. Billy wrote like that “I do want to write the composition different from the David’s. But my father is also David’s father. What I want to write about my father must be the same as David’s. So the following is the same as David’s. ”