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For centuries, explorers have risked their lives venturing into the unknown for reasons of economic benefit and national glory. Following the lunar missions of the early 1970s, Mars now looms as humanity’s next great, unknown land. But with dubious prospects for short-term financial return and with international competition in space a receding memory, it is clear that imperatives other than profit or national pride will have to compel human beings to leave their tracks on the planet’s red surface.With Mars the scientific benefits are perhaps higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by accumulating evidence that Mars once had abundant liquid water and by the controversy over suggestions that fossils of bacteria rode to Earth on a rock ejected from Mars during its early history. A definite answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. The revelation that life arose independently on Mars and on Earth would provide the first concrete clue in one of the deepest mysteries in all of science: how prevalent is life in our galaxyOne of the reasons why the idea of sending people to Mars strikes a chord in so many people is that it is already possible—the U.S. has the money and the fundamental technology needed to do it. More important, recent discoveries about the planet’s environment in the distant past have presented a clear and compelling scientific incentive for sending people: to search for evidence of life. The thesis that liquid water was once stable on Mars has been strengthened by aerial photographs taken last year that showed what appeared to be a drainage channel cut deeply by water flowing for hundreds if not thousands of years.A thorough hunt for any life on Mars that might be hanging on—despite the present deficit of water—would also have to be undertaken by humans, according to some experts. Such life will be hidden and probably tiny. "Finding it will require surveying vast tracts of territory," one expert explains. "It will require the ability to cover long distances and adapt to different conditions." Robots might be up to the task sometime in the distant future, making human explorers redundant, he concedes. But relying on them to survey Mars during periodical missions to the planet would take a very long time— "decades if not centuries," he believes. According to the passage, sending people to Mars is （）
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Although many factors affect human health during periods in space, weightlessness is the dominant and single most important one. The direct and indirect effects of weightlessness lead to a series of related responses. Ultimately, the whole body, from bones to brain, kidneys to bowels, reacts.When space travelers grasp the wall of their spacecraft and jerk their bodies back and forth, they say it feels as though they are stationary and the spacecraft is moving. The reason is based in our reliance on gravity to perceive our surroundings.The continuous and universal nature of gravity removes it from our daily notice, but our bodies never forget. Whether we realize it or not, we have evolved a large number of silent, automatic reactions to cope with the constant stress of living in a downward-pulling world. Only when we decrease or increase the effective force of gravity on our bodies do our minds perceive it.Our senses provide accurate information about the location of our center of mass and the relative positions of our body parts. Our brains integrate signals from our eyes and ears with other information from the organs in our inner ear, from our muscles and joints, and from our senses of touch and pressure.The apparatus of the inner ear is partitioned into two distinct components: circular, fluid-filled tubes that sense the angle of the head, and two bags filled with calcium crystals embedded in a thick fluid, which respond to linear movement. The movement of the calcium crystals sends a signal to the brain to tell us the direction of gravity. This is not the only cue the brain receives. Nerves in the muscles, joints, and skin—particularly the slain on the bottom of the feet—respond to the weight of limb segments and other body parts.Removing gravity transforms these signals. The inner ear no longer perceives a downward tendency when the head moves. The limbs no longer have weight, so muscles are no longer required to contract and relax in the usual way to maintain posture and bring about movement. Nerves that respond to touch and pressure in the feet and ankles no longer signal the direction of down. These and other changes contribute to orientation illusions, such as a feeling that the body or the spacecraft spontaneously changes direction. In 1961 a Russian astronaut reported vivid sensations of being upside down; one space shuttle specialist in astronomy said, "When the main engines cut off, I immediately felt as though we had inverted 180 degrees." Such illusions can recur even after some time in space. Which of the following apparatus of the body may be less affected by removing gravity（）
All great writers express their ideas in an individual way: it is often possible to determine the authorship of a literary passage from the style in which it is written; 46)Many authors feel that the conventions of the written language hamper them and they use words freely, with little observance of accepted grammar and sentence structure, in order to convey vividly their feelings, beliefs and fantasies. Others with a deep respect for traditional usage achieve a style of classical clearness and perfection or achieve effects of visual or musical beauty by their mastery of existing forms enriched by a sensitive and adventurous vocabulary, vivid imagery and a blending of evocative vowels and consonants.Young people often feel the need to experiment and, as a result, to break away from the traditions they have been taught. In dealing with a foreign language, however, they have to bear in mind two conditions for experiment. 47)Any great experimental artist is fully familiar with the conventions from which he wishes to break free: he is capable of achievement in established forms but feels these are inadequate for the expression of his ideas. In the second place, he is indisputably an outstanding artist who has something original to express; otherwise the experiments will appear pretentious, even childish.Few students can achieve so intimate an understanding of a foreign language that they can explore its resources freely and experimentally. Not all feel the need to do so. 48)And in any case examination candidates need to become thoroughly acquainted with conventional usage as it is a sure knowledge of accepted forms that examiners look for.The student undertaking a Proficiency course should have the ability to use simple English correctly to express everyday facts and ideas. 49)This ability to express oneself in a foreign language on a basis of thinking in that language without reference to one’s own is essential at all stages of learning. Students with extensive experience in translation who have had little practice in using the foreign language directly must, above all, write very simply at first, using only easy constructions which they are convinced are correct, forgetting for the time being their own language and rigorously avoiding translating from it.More complex forms, more varied vocabulary and sentence structure should evolve naturally in step with the student’s increasing knowledge of the language. The student introduces a certain form of construction only when he is thoroughly familiar with it and is certain that it is normally used in this way. As he achieves additional confidence, he can begin to take an interest in use of the language to create diverse effects. He may want to convey impressions of suspense, calm, dignity, humor, of music or poetry. 50) He will master the art of logical explanation, of exact letter writing, of formal speeches and natural conversation and of vivid impressionistic description. But he will still write within the limits of his ability and knowledge. And, as a learner, he will still be studying and observing conventional English usage in all that he writes. And in any case examination candidates need to become thoroughly acquainted with conventional usage as it is a sure knowledge of accepted forms that examiners look for.
It is widely believed that our never-ending quest for material goods is part of the basic character of human beings. According to the popular belief, we may not like it, but there’s little we can do about it.Despite its popularity, this view of human nature is wrong. While human beings may have a basic desire to strive towards something, there is nothing inevitable about material goods. There are numerous examples of societies in which things have played a highly restricted rule. In medieval Europe, the acquisition of goods was relatively unimportant. The common people, whose lives were surely poor by modern standards, showed strong preferences for leisure rather than money. In the nineteenth-and early twentieth-century United States, there is also considerable evidence that many working people also exhibited a restricted appetite for material goods.Materialism is not a basic trait of human nature, but a specific product of capitalism. With the development of the market system, materialism "spilled over", for the first time, beyond the circles of the rich. The growth of the middle class created a large group of potential buyers and the possibility that mass culture could be oriented around material goods. This process can be seen not only in historical experiences but is now going on in some parts of the developing world, where the growth of a large middle class has contributed to extensive materialism and the breakdown of traditional values.In the United States, the turning point was the 1920s—the point at which the "psychology of shortage" gave way to the "psychology of abundance". This was a crucial period for the development of modern materialism. Economy and discipline were out; waste and excess were in. Materialism flourished—both as a social ideology and in terms of high rates of real spending. In the midst of all this buying, we can detect the origins of modern consumer discontent.This was the decade during which the American dream, or what was then called "the American standard of living", captured the nation’s imagination. But it was always something of an illusion. Americans complained about items they could not afford—despite the fact that in the 1920s most families had telephones, virtually all had purchased life insurance, two-thirds owned their own homes and took vacations, and over half had motor cars.The discontent expressed by many Americans was promoted—and to a certain extent even created—by manufacturers. The explosion of consumer credit made the task easier, as automobiles, radios, electric refrigerators, washing machines—even jewelry and foreign travel—could be paid for in installments. By the end of the 1920s, 60 percent of cars, radios, and furniture were being purchased this way. The ability to buy without actually having money helped encourage a climate of instant satisfaction, expanding expectations, and ultimately, materialism. According to the passage, the practice of installment（）
For centuries, explorers have risked their lives venturing into the unknown for reasons of economic benefit and national glory. Following the lunar missions of the early 1970s, Mars now looms as humanity’s next great, unknown land. But with dubious prospects for short-term financial return and with international competition in space a receding memory, it is clear that imperatives other than profit or national pride will have to compel human beings to leave their tracks on the planet’s red surface.With Mars the scientific benefits are perhaps higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by accumulating evidence that Mars once had abundant liquid water and by the controversy over suggestions that fossils of bacteria rode to Earth on a rock ejected from Mars during its early history. A definite answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. The revelation that life arose independently on Mars and on Earth would provide the first concrete clue in one of the deepest mysteries in all of science: how prevalent is life in our galaxyOne of the reasons why the idea of sending people to Mars strikes a chord in so many people is that it is already possible—the U.S. has the money and the fundamental technology needed to do it. More important, recent discoveries about the planet’s environment in the distant past have presented a clear and compelling scientific incentive for sending people: to search for evidence of life. The thesis that liquid water was once stable on Mars has been strengthened by aerial photographs taken last year that showed what appeared to be a drainage channel cut deeply by water flowing for hundreds if not thousands of years.A thorough hunt for any life on Mars that might be hanging on—despite the present deficit of water—would also have to be undertaken by humans, according to some experts. Such life will be hidden and probably tiny. "Finding it will require surveying vast tracts of territory," one expert explains. "It will require the ability to cover long distances and adapt to different conditions." Robots might be up to the task sometime in the distant future, making human explorers redundant, he concedes. But relying on them to survey Mars during periodical missions to the planet would take a very long time— "decades if not centuries," he believes. The aerial photographs taken last year indicate that （）
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