题目内容：
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 a long
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 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 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 Gentral Pacifie Company,starting from
California,used Chinese labor,while the Union Pacific employed
crews of Irish labourers.The two groups worked at remunkable speed,euch trying to cover a greater distance than the other.In 1869 tay
met at a place called Promon
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