等差数列$\left\{a_n\right\}$的前n项和$S_n=a_1+a_2+\dots +a_n$，若$S_{10}=31,S_{20}=122$，则$S_{30}=$（   ）

发达国家在经历了20多年金融自由化后，金融危机重创了其过度膨胀的虚拟经济，危机后，发达国家纷纷出台了再工业化的政策，掀起了再工业化的浪潮。下图示意再工业化的动力机制。据此完成下列各题。

辽宁舰跑道长200m．飞机在航母上滑行的最大加速度为6m/s²，起飞需要的最低速度为50m/s．那么，飞机在滑行前，需要借助弹射系统获得的最小初速度为（   ）

根据短文理解，选择正确答案。

    The American literature is from the Romanticism to the Realism.

    The American Romanticism began from the end of 18th century to the outbreak of the Civil War, which is also called the American Renaissance. The period is as well as the time of American Westward Expansion. During the period, there were lots of workforces crowding to the cities, which promoted the industry.  The people found that they need their-own literature to record their experiences. So the Romanticism flourished(繁荣）.

    The Romanticism in American literature focuses on imagination and emotional factors. The American writers paid more attentions to the free expression of feelings and the characters' inner world. During the romantic period, there were many writers: Philip Freneau, William Cullen Bryant and so on.

    The Realism in American literature was from 1865 to 1914, and it takes on the American spirit, especially in American stories. The Realism against the Romanticism, advocates the people to come down to the earth and get rid of daydreams.

    During the 50 years from the Civil War to the WWI, the America had experienced a great change on many aspects, such as the politics, economy, culture and religion. It had changed the nature and the idea of the American society. The writers of new age didn't agree with the Romanticism of the old age.They were interested in real life and wanted to explain everything relating to the real life, which is to claim the objective reality, to get rid of idealism and Romanticism.

    There were 3 main writers at that time: William Peanoweils, Henry James and Mark Twain. Their writings represented the American native customs with their deep rural styles, which uncovered the people's inner life.