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For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain, Lewis and Clark journeyed into the American wilderness to find out what the U. S. had acquired when it purchased Louisianan, and the Apollo astronauts rocketed to the moon in a dramatic show of technological muscle during the cold war.Although their missions blended commercial and political-military imperatives, the explorers involved all accomplished some significant science simply by going where no scientists had gone before.Today Mars looms as humanity"s next great terra incognita (未探明之地). And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet"s reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role The question naturally invites a couple of others: are there experiment that only human could do on Mars Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary spaceWith Mars the scientific stakes are arguably 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 mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteorite (陨石) from Mars. A more conclusive 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. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science, the prevalence of life in the universe. The passage tells us that proof of life on Mars would ______.
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Most people think of lions as strictly African beasts, but only because they"re been killed off almost everywhere else. Ten thousand years ago lions spanned vast sections of the globe. Now lions hold only a small fraction of their former habitat, and Asiatic lions, a subspecies that split from African lions perhaps 100,000 years ago, hang on to an almost impossibly small slice of their former territory.India is the proud steward of these 300 or so lions, which live primarily in a 560-square-mile sanctuary (保护区). It took me a year and a half to get a permit to explore the entire Gir Forest—and no time at all to see why these lions became symbols of royalty and greatness. A tiger will hide in the forest unseen, but a lion stands its ground, curious and unafraid lionhearted. Though they told me in subtle ways when I got too close, Gir"s lions allowed me unique glimpses into their lives during my three months in the forest. It"s odd to think that they are threatened by extinction; Gir has as many lions as it can hold—too many, in fact. With territory in short supply, lions move about near the boundary of the forest and even leave it altogether, often clashing with people. That"s one reason India is creating a second sanctuary. There are other pressing reasons, outbreaks of disease or natural disasters. In 1994 a serious disease killed more than a third of Africa"s Serengeti lions—a thousand animals—a fate that could easily happen to Gir"s cats. These lions are especially vulnerable to disease because they descend from as few as a dozen individuals. "If you do a DNA test, Asiatic lions actually look like identical twins," says Stephen O"Brien, a geneticist (基因学家) who has studied them. Yet the dangers are hidden, and you wouldn"t suspect them by watching these lords of the forest. The lions display vitality, and no small measure of charm.Though the gentle intimacy of play vanishes when it"s time to eat, meals in Gir are not necessarily frantic affairs. For a mother and her baby lion sharing a deer, or a young male eating an antelope (羚羊), there"s no need to fight for a cut of the kill. The animals they hunt for food are generally smaller in Gir than those in Africa, and hunting groups tend to be smaller as well. One of the reasons why India is creating a secondary sanctuary for the Asiatic lions is that ______.
Every year television stations receive hundreds of complaints about the loudness of advertisements. However, federal rules forbid the practice of making ads louder than the programming. In addition, television stations always operate at the highest sound level allowed for reasons of efficiency. According to one NBC executive, no difference exists in the peak sound level of ads and programming. Given this information why do commercials sound so loudThe sensation of sound involves a variety of factors in addition to its speak level. Advertisers are skilful at creating the impression of loudness through their expert use of such factors. One major contributor to the perceived loudness of commercials is that much less variation in sound level occurs during a commercial. In regular programming the intensity of sound varies over a large range. However, sound levels in commercials tend to stay at or near peak levels.Other "tricks of the trade" are also used. Because low-frequency sounds can mask higher frequency sounds, advertisersfilter outany noises that may drown out the primary message. In addition, the human voice has more auditory (听觉的) impact in the middle frequency ranges. Advertisers electronically vary voice sounds so that they stay within such a frequency band. Another approach is to write the script so that lots of consonants are used, because people are more aware of consonants than vowel sounds. Finally, advertisers try to begin commercials with sounds that are highly different from those of the programming within which the commercial is buried. Because people become adapted to the type of sounds coming from programming, a dramatic change in sound quality draws viewer"s attention. For example, notice how many commercials begin with a cheerful song of some type.The attention-getting property of commercials can be seen by observing one-to two-year-old children who happen to be playing around a television set. They may totally ignore the programming. However, when a commercial comes on, their attention is immediately drawn to it because of its dramatic sound quality. One of the reasons why commercials are able to attract viewer attention is that ______.
Imagine a world in which there was suddenly no emotion—a world in which human beings could feel no love or happiness, no terror or hate. Try to imagine the consequences of such a transformation. People might not be able to stay alive: knowing neither joy nor pleasure, neither anxiety nor fear, they would be as likely to repeat acts that hurt them as acts that were beneficial. They could not learn: they could not benefit from experience because this emotionless world would lack rewards and punishments. Society would soon disappear: people would be as likely to harm one another as to provide help and support. Human relationships would not exist: in a world without friends or enemies, there could be no marriage, affection among companions, or bonds among members of groups. Society"s economic underpinnings (支柱) would be destroyed: since earning $10 million would be no more pleasant than earning $10, there would be no incentive to work. In fact, there would be no incentives of any kind. For as we will see, incentives imply a capacity to enjoy them.In such a world, the chances that the human species would survive are next to zero, because emotions are the basic instrument of our survival and adaptation. Emotions structure the world for us in important ways. As individuals, we categorize objects on the basis of our emotions. True we consider the length, shape, size, or texture, but an object"s physical aspects are less important than what it has done or can do to us—hurt us, surprise us, anger us or make us joyful. We also use categorizations colored by emotions in our families, communities, and overall society. Out of our emotional experiences with objects and events comes a social feeling of agreement that certain things and actions are "good" and others are "bad", and we apply these categories to every aspect of our social life—from what foods we eat and what clothes we wear to how we keep promises and which people our group will accept. In fact, society exploits our emotional reactions and attitudes, such as loyalty, morality, pride, shame, guilt, fear and greed, in order to maintain itself. It gives high rewards to individuals who perform important tasks such as surgery, makes heroes out of individuals for unusual or dangerous achievements, such as flying fighter planes in a war, and uses the legal penal (刑法的) system to make people afraid to engage in antisocial acts. According to the passage, people"s learning activities are possible because they ______.
For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain, Lewis and Clark journeyed into the American wilderness to find out what the U. S. had acquired when it purchased Louisianan, and the Apollo astronauts rocketed to the moon in a dramatic show of technological muscle during the cold war.Although their missions blended commercial and political-military imperatives, the explorers involved all accomplished some significant science simply by going where no scientists had gone before.Today Mars looms as humanity"s next great terra incognita (未探明之地). And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet"s reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role The question naturally invites a couple of others: are there experiment that only human could do on Mars Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary spaceWith Mars the scientific stakes are arguably 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 mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteorite (陨石) from Mars. A more conclusive 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. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science, the prevalence of life in the universe. By saying "With Mars the scientific stakes are arguably higher than they have ever been" (Line 1, Para. 4), the author means that ______.
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