Mr. Jenkins is fifty years old. He has taught math in a middle school for twenty-six years. He works hard and always come to his office on time. He hopes his students can be honest and is strict with them. Some of his students become famous persons,but they still remember him and often write to him. Of course the old man is proud of it. This term he began to teach Grade One. Some of the new students were told about him, but the others didn't know him well. He told them how to be an honest person. He gave them several examples and said,"I hate telling a lie most." Before class was over,he told all his students to finish Exercise 8 in Unit 1.The next morning,as soon as he came in the classroom,he asked,"Who's finished Exercise 8? " A few students put up their hands. He shook his head and said. "Open your workbooks and see if there's Exercise 8 in Unit 1 or not." The students had a look at their books and their faces turned red at once. Mr. Jenkins began to work in the school when he was   _  .
twenty-two twenty-three twenty-four twenty-five