A. add B. produce C. replace D. remove
65. Which of the following is the best title of the passage?
A. Tears are a sign of strong emotion.
B. Tears are always making us feel more comfortable.
C. Tears are uniquely human.
D. Tears have certain biological function.
B
The railroad industry could not have grown as large as it did without steel. The first rails were made of iron. But iron rails were not strong enough to support heavy trains running at a high speed. Railroad officials wanted to replace them with steel rails because steel was ten or fifteen times stronger and lasted twenty times longer. Before the 1870s, however, steel was too expensive to be widely used. It was made by a slow and expensive process of heating, stirring, and reheating iron ore(矿石).
Then the inventor Henry Bessemer discovered that directing a blast of air at melted iron in a furnace(熔炉)would burn out the impurities(杂质)that made the iron brittle(易脆). As the air shot through the furnace, the bubbling metal would erupt(喷发)in showers of sparks. When the fire cooled, the metal had been changed, or converted, to steel. The Bessemer converter made possible the mass production of steel, now three to five tons of iron could be changed into steel in a matter of minutes.
Just when the demand for more and more steel developed, prospectors discovered huge new deposits(矿床)of iron ore in the Mesabi Range, a 120-mile-long region in Minnesota near Lake Superior. The Mesabi deposits were so near the surface that they could be mined with steam shovels.
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