如何找出四级文章的中心思想3

    2．关于标题型
        Example :
         A rapid means of long-distance transportation became a necessity for the United States as settlement (新拓居地 ) spread ever farther westward. The early trains were impractical curiosities, and for along time the railroad companies met with troublesome mechanical problems. The most serious ones were the construction of rails able to bear the load, and the development of a safe, effective stopping system. Once these were solved, the railroad was established as the best means of land transportation. By 1860 there were thousands of miles of railroads crossing the eastern mountain ranges and reaching westward to the Mississippi. There were also regional southern and western lines .
        
         The high point in railroad building came with the construction of the first transcontinental system. In 1862 congress authorized two western railroad companies to build lines from Nebraska west-ward and from California eastward to a meeting point, so as to complete a transcontinental crossing linking the Atlantic seaboard with the Pacific .The Government helped the railroads generously with money and land Actual work on this project began four years later. money and land. Actual work on this project began four years later. The Central Pacific Company, starting from California, used Chinese labor, while the Union Pacific employed crews of Irish laborers. The two groups worked at remarkable speed, each trying to. cover a greater distance than the other. In l869 they met at a place called Promontory in what is now the state of Utah. Many visitors came there for the great occasion. There were joyous celebrations all the country, with parades and the ringing of church bells to honor the great achievement.
        
        The railroad was very important in encouraging westward movement. It also helped build up industry and farming by moving raw materials and by distributing products rapidly to distant markets. In linking towns and people to one another it helped unify the United States.
        
        the best title for this passage would be__________.
        A) Settlements Spread Westward
        B) The Coast-to-Coast Railroad: A Vital Link
        C) American Railroad History
        D) The Importance of Trains in the American Economy
        
         本题是给文章选标题，实际上也是问及全篇的主旨。文章第一段的第一句虽然提到"settlement spread ever farther westward "，但这不是本文论述的中心，故选项A）是错的；选项D）也不合适，因为作者在第三段第二句里谈的是在美国起重要作用的 transcontinental railway，而不是泛指美国的铁路；虽然本文从一个侧面反映了美国铁路的历史，故选项C)也是错的；本文的第三段点了文章的主旨，即这条横贯美国的铁路在开发西部、发展工农业生产和统一美国等方面起到了a vital link 的作用。因此，答案应该是选项B）。