单项选择题

Passage Three Questions 71 to 75 are based on the following passage: In the 1800s, trains roared into stations. They were symbols of progress and expansion. They played as much of a role in America’s history as presidents and generals. The first American railroads were built in the late 1820’s. The early railroads provided cheap transportation for shippers and travelers. To encourage the railroads to expand into unsettled land, President Millard Fillmore signed a series of landgrant acts (土地拨赠法案) in the 1850’s. These acts gave the railroad companies ownership of land that ran along the railways. In return for the land, the railroads carried government traffic at reduced rates. The railroad companies sold much of their land to farmers and cattlemen, who then shipped their goods on the trains. The importance of the railroads became clear during the Civil War. During the war, trains carried troops, arms, and supplies. One reason that the North won the war is that it had more use of the railroads. Between 1865 and 1900, railroads grew rapidly. The first transcontinental (跨越全洲的) route was completed in 1869. This track made easier for pioneers to cross the Rocky Mountains and settle the West. And the railroads brought new people to the West even before the trains started running. Thousands of Chinese and Irish laborers helped to lay down the tracks. Which of the following best expresses the main idea of the passage