A 50-year-old American officer came back to his school. The teacher asked him to give a talk to the small boys and girls there. The talk was about the love of their great country. All the little ones were sitting in a large meeting-room. The old officer went up and began speaking. He said , " Boys and girls . I studied in this school forty years ago. When I was your age, we were not as happy as you are today. Think about it and answer me, why are you so happy now?" No sound came from the children. The old man waited for a long time. Then a short boy in the front put up his small dirty hand. "Good boy! Please answer me, dear." said the officer. With a big smile on his face, the boy stood up and said, "If you speak long enough, we won't have Maths and biology lessons this morning." The officer studied in this school when he was  _  .
fifty ten twenty thirty