n the nucleus, but, until just before the outbreak of the Second World War, there was no way of releasing this energy in any large quantity. A revolutionary discovery was that, in certain circumstances, mass can be transformed into energy in accordance with Einstein's formula which states that the energy generated is equal to the mass lost multiplied by the square of the velocity of light.
The A-bomb, however, used a different process, depending upon radio-activity. In this process, called `fission', a heavier atom splits into two lighter atoms. In general, in radio-active substances this fission proceeds at a constant rate which is slow where substances occurring in nature are concerned. But there is one form of uranium called ‘U235’ which, when it is pure, sets up a chain reaction which spreads like fire, though with enormously greater rapidity. It is this substance which was used in making the atom bomb.
The political background of the atomic scientists' work was the determination to defeat the Nazis (德国纳粹). It was held – I think rightly – that a Nazi victory would be a terrible disaster. It was also held, in Western countries, that German scientists must be well advanced towards making an A-bomb, and that if they succeeded before the West did, they would probably win the war. When the war was over, it was discovered, to the complete astonishment of both American and British scientists, that the Germans were nowhere near success, and, as everybody knows, the Germans were defeated before any nuclear weapons had been made. But I do not think that nuclear scientists of the West can be blamed for thinking the work urgent and necessary. Even Einstein favored it.
When, however, the German war was finished, the great majority of those scientists who had worked together towards making the A-bomb considered that it should not be used against the Japanese, who were already on the verge of defeat and, in any case, did not constitute such a threat to the world as Hitler. Many of them made urgent representations to the American Government advocating that, instead of using the bomb as a weapon of war, they should, after a public announcement, explode it in a desert, and that future control of nuclear energy should be placed in the hands of an international authority. Seven of the most eminent of nuclear scientists drew up what is known as `The Franck Report' which they presented to the Secretary of War in June 1945. This is a very admirable and far-seeing document, and if it had won the assent of the politicians, none of our subsequent terrors would have arisen.
66. We may infer that the writer’s attitude towards the A-bomb is that __________.
A. it is a terrible threat to the whole of mankind
B. it played a vital part in defeating the Japanese
C. it was a wonderful invention
D. it is a necessary evil
67. According to the passage, an atom is heavy if _________.
A. it is radio-active
B. it has a large nucleus
C. its nucleus has many electrons
D. its nucleus shoots out many particles
68. The American and British scientists were astonished at the end of the Second World War against Germany because ____________.
A. the Germans had been defeated without the use of nuclear weapons
B. the Western countries had won before they had invented nuclear weapons
C. they thought the Germans would probably win the war
D. the Germans had made little progress in developing nuclear weapons
69. According to the writer, most scientists who had helped in making the A-bomb considered that it should not be used against the Japanese because __________.
A. it was such a dangerous weapon
B. its use against the Japanese was unnecessary
C. it was a very inhumane weapon
D. the German war was finished
70. It is implied that the nuclear scientists __________.
A. might not have agreed to develop the bomb if there had been no Nazi threat
B. would have developed the bomb even without the Nazi threat
C. would have made the bomb, under peace-time conditions, but only for the use of an international authority
D. developed the bomb because Einstein thought it urgent and necessary
E
Increasingly, over the past ten years, people ?- especially young people -- have become aware of the need to change their eating habits, because much of the food they eat, particularly processed foods, is not good for the health. Consequently, there has been a growing interest in natural foods: foods which do not contain chemical additives and which have not been affected by chemical fertilizers widely used in farming today.
Natural foods, for example, are vegetables, fruit and grain which have been grown in soil that is rich in organic matter. In simple terms, this means that the soil has been nourished by unused vegetable matter, which provides it with essential vitamins and minerals. This in itself is a natural process compared with the use of chemicals and fertilizers, the main purpose of which is to increase the amount -? but not the quality -? of foods grown in commercial farming areas.
Natural foods also include animals which have been allowed to feed and move freely in healthy pastures. Compare this with what happens in the mass production of poultry: there are battery (养鸡房) farms, for example, where thousands of chickens live crowded together in one building and are fed on food which is little better than rubbish. Chickens kept in this way are not only tasteless as food; they also produce eggs which lack important vitamins.
There are other aspects of healthy eating which are now receiving increasing attention from experts on diet. Take, for example, the question of sugar. This is actually a non?essential food! Although a natural alternative, such as honey, can be used to sweeten food if this is necessary, we can in fact do without it. It is not that sugar is harmful in itself. But it does seem to be addictive (易成瘾的): the qua 上一页 [1] [2] [3] [4] [5] 下一页
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