These diamond were probably carried from where they were formed to India．

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更多“These diamond were probably ca…”相关的问题

第1题

"It should be possible to make a precious stone that not only looks like the real thing, b

ut that is the real thing", said a chemist many years ago. "The only difference should be that one crystal would be made by man, the other by nature."

At first this did not seem like a particularly hard task. Scientists began to try making synthetic diamonds towards the end of the eighteenth century. It was at this time that a key scientific fact was discovered: diamonds are a form. of carbon, which is a very common element. Graphite, the black mineral that is used for the lead in your pencil, is made of it, too. The only difference, we know today, is that the carbon atoms have been packed together in a slightly different way. The chemists were fired with enthusiasm: Why not change a cheap and plentiful substance, carbon, into a rare and expensive one, diamond？

You have probably heard about the alchemists who for centuries tried to turn plain lead or iron into gold. They failed because gold is completely different from lead or iron. Transforming carbon into diamonds, however, is not illogical at all. This change takes place in nature, so it should be possible to make it happen in the laboratory.

It should be possible, but for one hundred and fifty years efforts failed. During this period, none the less, several people believed that they had solved the diamond riddle. One of these was a French scientist who produced crystals that seemed to be the real thing. After the man's death, however, a curious rumour began to go the rounds. The story told that one of the scientist's assistants had simply put tiny pieces of genuine diamonds into the carbon mixture. He was bored with the work, and he wanted to make the old chemist happy.

The first real success came more than sixty years later in the laboratories of the General Electric Company. Scientists there had been working for a number of years on a process designed to duplicate nature's work. Far below the earth's surface, carbon is subjected to incredibly heavy pressure and extremely high temperature. Under these conditions the carbon turns into diamonds. For a long time the laboratory attempt failed, simply because no suitable machinery existed. What was needed was some sort of pressure chamber in which the carbon could be subjected to between 800,000 and 1,800,000 pounds of pressure to the square inch, at a temperature of between 200°F and 2,200°F.

Building a pressure chamber that would not break under these conditions was a fantastically difficult feat, but eventually it was done. The scientists eagerly set to work again. Imagine their disappointment when, even with this equipment, they produce all sorts of crystals, but no diamonds. They wondered if the fault lay in the carbon they were using, and so they tried a number of difficult forms. They failed again and again but went on working. The idea was then brought forward that perhaps the carbon needed to be dissolved in a melted metal. The metal might act as a catalyst, which means that it helps a chemical reaction to take place more easily.

This time the carbon was mixed with iron before being placed in the pressure chamber. The pressure was brought up to 1,100,000 pounds to the square inch and the temperature to 900℉. At last the chamber was opened. A number of shiny crystals lay within. These crystals scratched glass, and even diamonds. Light waves passed through them in the same way as they do through diamonds. Carbon dioxide was given off when the crystals were burned. Their density was just 3.5 grams per cubic centimeter, as is true of diamonds. The crystals were analyzed chemically. They were finally studied under X-rays, and there was no longer room for doubt. These jewels of the laboratory were not like diamonds; they were diamonds. They even had the same atomic structure.

The main idea of Paragraph 2 is that______.

A．making artificial diamonds didn't seem very difficult at first sight

B．scientists began to try making synthetic diamond in the late 1700s

C．scientists discovered diamonds are a form. of carbon, a common element

D．the discovery of the diamonds' constitute impelled scientists to make a synthetic one

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第2题

The liberal view of democratic citizenship that developed in the 17th and 18th centuries w

as fundamentally different from that of the classical Greeks. The pursuit of private interests with as little interference as possible from government was seen as the road to human happiness and progress rather than the public obligations and involvement in the collective community that were emphasized by the Greeks. Freedom was to be realized by limiting the scope of governmental activity and political obligation and not through immersion in the collective life of the polis. The basic role of the citizen was to select governmental leaders and keep the powers and scope of public authority in check. On the liberal view, the. rights of citizens against the state were the focus of special emphasis.

Over time, the liberal democratic notion of citizenship developed in two directions. First, there was a movement to increase the proportion of members of society who were eligible to participate as citizens--especially through extending the right of suffrage--and to ensure the basic political equality of all. Second, there was a broadening of the legitimate activities of government and a use of governmental power to redress imbalances in social and economic life. Political citizenship became an instrument through which groups and classes with sufficient numbers of votes could use the state power to enhance their social and economic well-being.

Within the general liberal view of democratic citizenship, tensions have developed over the degree to which government can and should be used as an instrument for promoting happiness and well-being. Political philosopher Martin Diamond has categorized two views of democracy as follows. On the one hand, there is the "libertarian" perspective that stresses the private pursuit of happiness and emphasizes the necessity for restraint on government and protection of individual liberties. On the other hand, there is the "majoritarian" view that emphasizes the "task of the government to uplift and aid the common man against the malefactors of great wealth." The tensions between these two views are very evident today. Taxpayer revolts and calls for smaller government and less government regulation clash with demands for greater government involvement in the economic marketplace and the social sphere.

The author's primary purpose is to ______.

A．study ancient concepts of citizenship

B．contrast different notions of citizenship

C．criticize modern libertarian democracy

D．describe the importance of universal suffrage

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第3题

The old buildings were restored to their（)condition.

A.original

B.first

C.before

D.p ast