6、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 (礦石).

Then the inventor Henry Bessemer discovered that directing a blast of air at melted iron in a furnace (熔爐) would burn out the impurities (雜質(zhì)) that made the iron brittle (易脆). As the air shot through the furnace, the bubbling metal would erupt (噴發(fā)) 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 (礦床) 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.

Barges and steamers carried the iron ore through Lake Superior to deposits on the southern shores of Lake Michigan and Lake Erie. With dizzying speed Gary, Indiana and Toledo, Youngstown, and Cleveland, Ohio, became major steel manufacturing centers. Pittsburgh was the greatest steel city of all.

1．The best title for the passage is ____.

       A．The railroad Industry                           B．Famous Inventors

       C．Changing Iron into Steel                       D．Steel Manufacturing Centers

2．According to the passage, how did the Bessemer method make the mass production of steel possible?

       A．It directed air at melted iron in furnace, removing all impurities.

       B．It slowly heated iron ore, then stirred it and heated it again.

       C．It changed iron ore into iron, which was a substitute (替代物) for steel.

       D．It could be quickly found deposits of iron ore under the ground.

3．It can be inferred from the passage that the mass production of steel caused ____.

       A．a(chǎn) decline in the railroad industry      

       B．a(chǎn) revolution in the industrial world

       C．a(chǎn)n increase in the price of steel        

       D．a(chǎn) feeling of discontent among steel workers