Passage
　　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 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 railroads 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 labourers. The two groups worked at remarkable speed, each trying to cover a greater distance than the other. In 1869 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 over the country, with parades and the ringing of church bells to honor the great achievement.
　　The construction of the transcontinental railroad took_.
　　A. 9 years B. 7 years C. 4 years D. 3 years

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