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  3. When aluminum was first produced about a hundred and fifty years ago, it was so difficult to separate from the ores(矿石) in which

When aluminum was first produced about a hundred and fifty years ago, it was so difficult to separate from the ores(矿石) in which

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问题     When aluminum was first produced about a hundred and fifty years ago, it was so difficult to separate from the ores(矿石) in which it was found that its price was higher than that of gold. The price remained high until a new process was discovered for refining the metal with the aid of electricity approximately three quarters of a century later. The new method was so much cheaper that aluminum became practical for many purposes, one of which was making pots and pans.
    Aluminum is lightweight, rustproof and easily shaped into different forms. By mixing it with other metals, scientist have been able to produce a variety of alloys, some of which have the strength of steel but weigh only one third as much.
    Today, the uses of aluminum are innumerable. Perhaps its most important use is in transportation. Aluminum is found in the engines of automobiles, in the hulls of boats. It is also used in many parts of airplanes. In fact, the huge "airbus" planes would probably never have been produced if aluminum did not exist. By making vehicles lighter in weight aluminum has greatly reduced the amount of fuel needed to move them. Aluminum is also being used extensively in the building industry in some countries.
    Since aluminum is such a versatile(多用的) metal, it is fortunate that bauxite(铝土矿) , which is one of its chief sources, is also one of the earth’s most plentiful substances. As the source of aluminum is almost inexhaustible, we can expect that more and more uses will be found for this versatile metal.
The price of aluminum was sharply reduced when people discovered a new refining process with the aid of______.
选项 A、wind power
B、solar energy
C、hydraulic power
D、electricity
答案D
解析 根据第一段第二句里中的with the aid of electricity(有了电的帮助)，所以正确的选项为D。A项意为“风能”，B项意为“太阳能”，C项意为“水能”。
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