材料一：我国是世界上人口最多的国家，随着我国人口老龄化程度的不断加深，老年人口数量占全国总人口数量的比重将不断增长。

一国人口生育率的迅速下降在造成人口老龄化加速的同时，也将导致少儿抚养比例迅速下降，劳动年龄人口比例上升。在老年人口比例达到较高水平之前，将形成一个劳动力资源相对丰富、抚养负担轻、对经济发展十分有利的“黄金时期”，这一现象被称为“人口红利”。

材料二：随着综合国力的提高，我国外交从建国初的“一边倒”演变到“构建人类命运共同体”，诚如***主席说过“只有各国共同发展了，世界才能更好发展。那种以邻为壑、转嫁危机、损人利己的做法既不道德，也难以持久。”我国从建国初期的“一穷二白”，经历十二个五年规划，发展到全世界第二大经济体，也越来越意识到中国的世界责任，在世界秩序中发出越来越多的中国声音。9月3日，在纪念中国人民抗日战争暨世界反法西斯战争胜利70周年阅兵式上，***主席宣布中国将裁军30万；在9月26日联合国发展峰会上，宣布设立南南合作援助基金，首期提供20亿美元;在9月27日全球妇女峰会上，向联合国妇女署捐款1000万美元，落实2015年后发展议程相关目标。

阅读理解

    In 1999, twelve percent of public elementary schools in the United States required students to wear uniforms. Just three years later, the amount was almost double that.

    A study of six big-city Ohio public schools showed students who were required to wear uniforms had improved graduation, behavior and attendance rates. Academic performance was unchanged.

    Some high schools in Texas have also joined in the movement. Yet studies find mixed results from requiring uniforms. And some schools have turned away from such policies.

    Supporters believe dressing the same creates a better learning environment and safer schools. The school district in Long Beach, California, was the first in the country to require uniforms in all elementary and middle schools. The example helped build national interest in uniforms as a way to deal with school violence and improve learning.

    Findings in Long Beach suggested that the policy resulted in fewer behavior problems and better attendance. But researcher Viktoria, who has looked at those findings, says they were based only on opinions about the effects of uniforms.

    She says other steps taken at the same time to improve schools in Long Beach and statewide could have influenced the findings. The district (the area marked by government) increased punishments for misbehavior. And California passed a law to reduce class sizes.

    In Florida, for example, researcher Sharon found that uniforms seemed to improve behavior and reduce violence. In Texas, Eloise found fewer discipline problems among students required to wear uniforms, but no effect on attendance.

    Sociologist David has studied school uniform policies since1998.He collected the reports in the book. In his own study, he found that reading and mathematics performance dropped after a school in Pennsylvania（宾夕法尼亚州）required uniforms.

    Political and community pressures may persuade schools to go to uniforms to improve learning. But David and others believe there is not enough evidence of a direct relationship. In fact, he says requiring uniforms may even increase discipline problems.

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内。

    A year ago, I paid no attention to English idioms（习语）, though my teacher told us the importance again and again. But soon, the importance of English idioms was shown in an amusing experience.
    One day, I happened to meet an Englishman on the road, and soon we began to talk. As I was talking about how I was studying English, the foreigner seemed to be surprised. Gently shaking his head，shrugging his shoulders, he said，“You don't say!” “You don't say!” I was puzzled. I thought, perhaps this is not a right topic. “Well, I’d better change the topic.” So I said to him. “Well, shall we talk about the Great Wall? By the way, have you ever been there?” “Certainly, everyone back home will laugh at me if I leave China without seeing it. It was wonderful.” He was deep in thought when I began to talk like a tourist guide. “The Great Wall is one of the wonders in the world. We are very proud of it.” Soon I was interrupted（打断）again by his words: “You don't say!” I couldn't help asking, “Why do you ask me not to talk about it?” “Well, I didn't ask you to do so,” he answered, greatly surprised. I said, “Didn't you say ‘you don't say’?” Hearing this, the Englishman laughed to tears. He began to explain, “ ‘You don't say’ actually means ‘really!’ It is an expression of surprise. Perhaps you don't pay attention to English idioms.” I realized I had made a fool of myself. Since then I have been more careful with idiomatic expressions. Remember: what the English teachers said is always right to us students.

—What's your New Year's resolution, Dave?

—I'm going to exercise more _______.

已知直角三角形两边的长分别为3cm,4cm, 则以第三边为边长的正方形的面积为____