设$A=\left(\begin{array}{cc}1& 1\\ 4& 1\end{array}\right)$，则矩阵$A$的一个特征值$\lambda$和对应的一个特征向量$\overrightarrow{a}$为（   ）

材料一：在19世纪下半叶，以英镑为中心的国际贸易和投资体系覆盖全球，90%的国际支付以英镑进行，而印度等国的中央银行则直接持有英镑而不是黄金，“英镑等同于黄金几乎是天经地义的事”。

——钟伟《国际货币体系的百年变迁和远瞻》

材料二：美国成为强国的历程始于18世纪末，结束于20世纪初。美国……东西两侧濒临大洋，且幅员辽阔，资源丰富。独立革命期间，它利用英法矛盾，获得外援并赢得独立。……两次世界大战期间，美国扩大生产和黄金储备；战后又在军事高科技领域不断创新，抓住信息革命的机遇成为新经济的领头羊。美国拥有世界上最早实行而且最有连续性的成文宪法，宪政体制稳定。……在全球化大背景下，不断补充的人才，各种文化的碰撞，融合和发酵，为社会发展提供了巨大动力。

——李剑鸣《美国历史》

材料三：从1948年到1974年全球衰退开始的25年间，西欧经济经历了前所未有的不间断增长。欧洲人后来把这段时期称为“白银的50年代”和“黄金的60年代”。西欧的繁荣来源于竞争性的、资本主义的、自由市场的和私营企业制度的经济。但是几乎在所有的国家，这一时期的繁荣也都不同程度上伴随着广泛的经济计划、系统的政府干预，以及用以克服竞争性资本主义和商业周期的不稳定的社会服务体系。

——帕尔默《现代世界史》

材料四：在各国走向繁荣昌盛的途程中有一些共同的因素起着关键性的作用，而对这些共同因素的偏离，不论这种偏离朝向哪个方向，总会招致逆转和挫折。通观500年来世界各主要国家的发展历程，这些共同的要素大致包括以下这些：

①确立了自由市场经济制度；

②建立了法治；

③实行宪政民主；

④保证思想自由和学术独立；

⑤“橄榄形社会结构”的逐步形成（中等阶层的兴起使传统两头大、中间小的“哑铃形社会”转化为现代两头小、中间大的“橄榄形社会”。“哑铃形社会”通常是不稳定的、充满了动乱，而“橄榄形社会”则趋于稳定）。

——吴敬琏《从<大国崛起>看各国富强之道》

    If you are interested in studying at an American university, you have to take the Test of English as a Foreign Language. The test is widely known as the TOEFL. It is the most widely used language exam for American universities.

    There are two major kinds of the TOEFL test. The first is the IBT，or Internet based Test. It is offered in most of the world and accepted by nearly every university and scholarship program in the United States. The other kind of the test is called the Paper­based Test or PBT. The PBT is less costly to take and does not require use of the Internet.

    But how to get started with TOEFL? Here are some tips.

    ⒈Plan ahead — It takes a long time to improve your TOEFL score. Do not expect a big lift in your test results after two weeks. You will have to spend a lot of time and energy.

    ⒉Master the basics first — You should have to be good at basic English before you take the test. If you score below 500 on the PBT or 70 on the IBT, study for a few months and come back to the TOEFL later.

    ⒊Get a study guide — It is easy to find study guides for the IBT. Pearson, Barron's, ETS, and Kaplan all produce quality materials, take a practice test once or twice a month. The best study guides will have explanations in the answer key.

    ⒋Use outside resources — Remember, you are learning a language, not a test. You can improve your TOEFL score by making English part of your daily life. Some simple ways are listening to English speakers, watching movies and reading newspapers. Some others are reading English textbooks, sending and reading text messages in English, and writing online in English.

    The best way to do well on the TOEFL is to know English well. The real goal of the test is to measure how well a student can communicate in English­speaking classroom.

    If you want to know more, please click here.

“黄梅时节家家雨 青草池塘处处蛙”形象地描述了那种天气（　　）