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At the present time, 98 percent of the world energy consumption comes from stored sources, such as fossil fuels or nuclear fuel. Only hydroelectric and wood energy represent completely renewable sources on ordinary time scales. Discovery of large additional fossil fuel reserves, solution of the nuclear safety and waste disposal problems, or the development of controlled thermonuclear fusion will provide only a short-term solution to the world"s energy crisis. Within about 100 years, the thermal pollution resulting from our increased energy consumption will make solar energy a necessity at any cost.Man"s energy consumption is currently about one part in ten thousand that of the energy we receive from the sun. However, it is growing at a 5 percent rate, of which about 2 percent represents a population growth and 3 percent a per capita energy increase. If this growth continues, within 100 years our energy consumption will be about 1 percent of the absorbed solar energy, enough to increase the average temperature of the earth by about one degree centigrade if stored energy continues to be our predominant source. This will be the point at which there will be significant effects in our climate, including the melting of the polar ice caps, a phenomenon which will raise the level of the oceans and flood parts of our major cities. There is positive feedback associated with this process, since the polar ice cap contributes to the partial reflectivity of the energy arriving from the sun. As the ice caps begin to melt, the reflectivity will decrease, thus heating the earth still further.It is often stated that the growth rate will decline or that energy conservation measures will preclude any long-range problem. Instead, this only postpones the problem by a few years. Conservation by a factor of two together with a maintenance of the 5 percent growth rate delays the problem by only 14 years. Reduction of the growth rate to 4 percent postpones the problem by only 25 years; in addition, the inequities in standards of living throughout the world will provide pressure toward an increase in growth rate, particularly if cheap energy is available. The problem of a changing climate will not be evident until perhaps ten years before it becomes critical due to the nature of an exponential growth rate together with the normal annual weather variations. This may be too short a period to circumvent the problem by converting to other energy sources, so advance planning is a necessity.The only practical means of avoiding the problem of thermal pollution appears to be the use of solar energy. Using the solar energy before it is dissipated to heat does not increase the earth"s energy balance. The cost of solar energy is extremely favorable now, particularly when compared to the cost of relocating many of our major cities. The positive feedback mentioned in the second paragraph means that the melting of the polar ice caps will ______.
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请简述《义务教育语文课程标准(2011年版)》第三学段对综合性教学的要求。
Most American politicians say they support marriage, but few do much about it, except perhaps to sound off about the illusory threat to it from gays. The public are divided. Few want to go back to the attitudes or divorce laws of the 1950s. But many at both ends of the political spectrum lament the fragility of American families and would change, at least, the way the tax code penalises many couples who marry. And some politicians want the state to draw attention to benefits of marriage, as it does to the perils of smoking. George Bush is one.Since last year, his administration has been handing out grants to promote healthy marriages. This is a less preachy enterprise than you might expect. Sidonie Squier, the bureaucrat in charge, does not argue that divorce is wrong: "If you"re being abused, you should get out." Nor does she think the government should take a view on whether people should have pre-marital sex.Her budget for boosting marriage is tiny: $100m a year, or about what the Defence Department spends every two hours. Some of it funds research into what makes a relationship work well and whether outsiders can help. Most of the rest goes to groups that try to help couples get along better, some of which are religiously-inspired. The first 124 grants were disbursed only last September, so it is too early to say whether any of this will work. But certain approaches look hopeful.One is "marriage education". The army already does this. About 35,000 soldiers this year will get a 12-hour course on how to communicate better with their partners, and how to resolve disputes without throwing plates. It costs about $300 per family. Given that it costs $50,000 to recruit and train a rifleman, and that marital problems are a big reason why soldiers quit, you don"t have to save many marriages for this to be cost-effective, says Peter Frederich, the chaplain in charge.Several studies have shown that such courses do indeed help couples communicate better and quarrel less bitterly. As to whether they prevent divorce, a meta-analysis by Jason Carroll and William Doherty concluded that the jury was still out. The National Institutes of Health is paying for a five-year study of Mr Frederich"s soldiers to shed further light on the issue.At the end of the day, says Ms Squier, the government"s influence over the culture of marriage will be marginal. Messages from movies, peers and parents matter far more. But she does not see why, for example, the government"s only contact with an unmarried father should be to demand that he pay child support. By not even mentioning marriage, the state is implying that no one expects him to stick around. Is that a helpful message President George Bush would try to save the married life by ______.
When our children are born, we study their every eyelash and marvel at the perfection of their toes, and in no time become experts in all that they do. But then the day comes when we are expected to hand them over to a stranger standing at the head of a room full of bright colors and small chairs. Well aware of the difference a great teacher can make—and the damage a bad teacher can do—parents turn over their kids and hope. Please handle with care. Please don"t let my children get lost. They"re breakable. And precious. Oh, but push them hard and don"t let up, and make sure they get into Harvard.But if parents are searching for the perfect teacher, teachers are looking for the ideal parent, a partner but not a pest, engaged but not obsessed, with a sense of perspective and patience. And somehow just at the moment when the experts all say the parent-teacher alliance is more important than ever, it is also becoming harder to manage. At a time when competition is rising and resources are strained, when battles over testing and accountability force schools to adjust their priorities, when cell phones and e-mail speed up the information flow and all kinds of private ghosts and public quarrels creep into the parent-teacher conference, it"s harder for both sides to step back and breathe deeply and look at the goals they share.Ask teachers about the best part of their job, and most will say how much they love working with kids. Ask them about the most demanding part, and they will say dealing with parents. In fact, a new study finds that of all the challenges they face, new teachers rank handling parents at the top. According to preliminary results from the MetLife Survey of the American Teacher, parent management was a bigger struggle than finding enough funding or maintaining discipline or enduring the toils of testing. It"s one reason that 40% to 50% of new teachers leave the profession within five years. Even master teachers who love their work call this "the most treacherous part of their jobs.""Everyone says the parent-teacher conference should be pleasant, civilized, a kind of dialogue where parents and teachers build alliances," Lawrence-Lightfoot observes. "But what most teachers feel, and certainly what all parents feel, is anxiety, panic and vulnerability." While teachers worry most about the parents they never see, the ones who show up faithfully pose a whole different set of challenges. "I could summarize in one sentence what teachers hate about parents," says the head of a private school. "We hate it when parents undermine the education and growth of their children. That"s it, plain and simple." The word "pest" (first sentence, Para.2) probably refers to ______.
春望 杜甫 国破山河在，城春草木深。 感时花溅泪，恨别鸟惊心。 烽火连三月，家书抵万金。 白头搔更短，浑欲不胜簪。 这首诗，首联描写“城春草木深”的景象有什么用意 从全诗来看，诗人“白头搔更短”的原因是什么
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