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A．asB．thatC．in orderD．quickly
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If it were only necessary to decide whether to teach elementary science to everyone on a mass basis or to find the gifted few and take them as far as they can go, our task would be fairly simple. The public school system, however, has no such choice, for the jobs must be carried on at the same time. Because we depend so heavily upon science and technology for our progress, we must produce specialists in many fields. Because we live in a democratic nation, whose citizens make the policies for the nation, large numbers of us must be educated to understand, to support, and when necessary, to judge the work of experts. The public school must educate both producers and users of scientific services.
In education, there should be a good balance among the branches of knowledge that contribute to effective thinking and wise judgment. Such balance is defeated by too much emphasis on any one field. This question of balance involves not only the relation of the natural sciences, the social sciences, and the arts but also relative emphases among the natural sciences themselves.
Similarly, we must have a balance between current and classical knowledge. The attention of the public is continually drawn to new possibilities in scientific fields and the discovery of new knowledge; these should not be allowed to mm our attention away from the sound, established materials that form. the basis of courses for beginners.
According to the first paragraph, the task of education is fairly complicated because ______.
Magnesium is another mineral we now obtain by collecting huge volumes of ocean water and treating it with chemicals. Although originally it was derived only from brines or from the treatment of such magnesium-containing rocks as dolomite, of which whole mountain ranges are composed. In a cubic mile of sea water there are about four million tons of magnesium. Since the direct extraction method was developed about 1941, production has increased enormously. It was magnesium from sea that made possible the wartime growth of the aviation industry, for every, air plane made in the United States (and in most other countries as well) contains about haft a ton of magnesium metal. And it has innumerable uses in other industries where a lightweight metal is desired, besides its long-standing utility as an insulating material, and its use in printing inks, medicines, and toothpaste.
What is the main topic of this passage？
The author is an aggressive, brilliant and literate astronomer. This vastly entertaining book has a simple manner with complex ideas, without being patronizing, and is often very funny.
In 274 pages Sagan deals with everything from the formation of the Earth to the puzzling possibilities of contact with extra-terrestrial life. This is the moment in history when man's stepping into the universe has suddenly become conceivable. To Sagan this is more exciting and important than was the exploration of the New World in the sixteenth century. So expenditure on the space programme, pruned of recent excesses, ought to continue--it is, according to Sagan, no larger a part of America's gross national income than was the relative cost to England in the sixteenth century of exploration in sailing ships.
The book is not for scientific illiterates, nor is Sagan a pedestrian scientist. Although he makes short work of the unidentified foreign objects (UFO) spotters, he is unafraid to take us on a speculative journey to a black hole which, for all he knows, might be the quick route to somewhere else, not necessarily our universe.
Sagan exhibits a passionate interest in life in the cosmos in which there are .almost certainly civilizations much more advanced than our own. We are the result of a number of relatively recent cosmic accidents, but for all that, Sagan is no less excited about our future,
From the passage we understand that Carl Sagan writes ______.
上海证券交易所会员在证券登记结算公司的资金交收账户出现透支，如在T+2下午17:00之前未能弥补，则每天按透支金额的0.4%处以罚款。()
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