题目内容：
12. (阅读理解题)Section B
A rapid means of long-distance transportation became a necessity for the United States as settlement spread ever farther west-ward. The early trains were impractical curiosities, and for a long time the railroad companies met with troublesome mechanical problems. The most serious ones were the construction of rails able to bear the road, 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 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 1860 Congress authorized two western railroad companies to build lines from Nebraska westward 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 railroad generously with 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 1869 they met at a
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