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What are the chances that we will encounter some alien form of life, as we explore the galaxy.If the argument about the time scale for the appearance of life on Earth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before the Earth. So why is the galaxy not crawling with self designing mechanical or biological life forms Why hasn’t the Earth been visied, and even colonized. I discount suggestions that UFOs contain beings from outer space. I think any visits by aliens would be much more obvious, and probably also, much more unpleasant. What is the explanation of why we have not been visited One possibility is that the argument about the appearance of life on Earth is wrong. Maybe the probability of life spontaneously appearing is so low that Earth is the only planet in the galaxy, or in the observable universe, in which it happened. Another possibility is that there was a reasonable probability of forming self-reproducing system, like cells, but most of these forms of life did not evolve intelligence. A third possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, in the external transmission phase. But at that point, the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true. I prefer a fourth possibility: there are other forms of intelligent life out there, but we have been overlooked. There used to be a project called SETI, the search for extraterrestrial intelligence. It involved scanning the radio frequencies, to see if we could pick up signals from alien civilizations. I thought this project was worth supporting, though it was cancelled due to a lack of funds. But we should have been wary of answering back, until we have developed a bit further. Meeting a more advanced civilization, at our present stage, might be a bit like the original inhabitants of America meeting Columbus. I don’t think they were better off for it. The author thinks that______.
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Many theories concerning the causes of juvenile delinquency (crimes committed by young people) focus either on the individual or on society as the major contributing influence. Theories (21) on the individual suggest that children engage in criminal behavior (22) they were not sufficiently penalized for previous misdeeds or that they have learned criminal behavior through (23) with others. Theories focusing on the role of society suggest that children commit crimes in (24) to their failure to rise above their socioeconomic status, (25) as a rejection of middle-class values. Most theories of juvenile delinquency have focused on children from disadvantaged families, (26) the fact that children from wealthy homes also commit crimes. The latter may commit crimes (27) lack of adequate pa- rental control. All theories, however, are tentative and are (28) to criticism. Changes in the social structure may indirectly (29) juvenile crime rates. For example, changes in the economy that (30) to fewer job opportunities for youth and rising unemployment (31) make gainful employment increasingly difficult to obtain. The resulting discontent may in (32) lead more youths into criminal-behavior. Families have also (33) changes these years. More families consist of one-parent households or two working parents; (34) , children are likely to have less supervision at home (35) was common m the traditional family structure. 31（）
"Before, we were too black to be white. Now, we’re too white to be black." Hadija, one of South Africa’s 3.5m Coloured (mixed race) people, sells lace curtains at a street market in a bleak township outside Cape Town. In 1966 she and her family were driven out of District Six, in central Cape Town, by an apartheid government that wanted the area for whites. Most of the old houses and shops were bulldozed but a Methodist church, escaping demolition, has been turned into a little museum, with and old street plan stretched across the floor. On it, families have identified their old houses, writing names and memories in bright felt-tip pen. "We can forgive, but not forget," says one.Up to a point. In the old days, trampled on by whites, they were made to accept a second-class life of scant privileges as a grim reward for being lighter-skinned than the third-class blacks. Today, they feel trampled on by the black majority. The white-led National Party; which still governs the Western Cape, the province where some 80% of Coloureds live, plays on this fear to good electoral effect. With no apparent irony, the party also appeals to the Coloured sense of common culture with fellow Afrikaans-speaking whites, a link the Nats have spent decades denying.This curious courtship is again in full swing. A municipal election is to be held in the province on May 29th and the Nats need the Coloured vote if they are to win many local councils.By most measures, Coloureds are still better-off than blacks. Their jobless rate is high, 21% according to the most recent figures available. But the black rate is 38%. Their average yearly income is still more than twice that of blacks. But politics turns on fears and aspirations. Most Coloureds fret that affirmative action, the promotion of non-whites into government-related jobs, is leaving them behind. Affirmative action is supposed to help Coloureds (and Indians) too. It often does not. They may get left off a shortlist because, for instance, a job requires the applicant to speak a black African language, such as Xhosa.Some Coloureds think that the only way they will improve their lot is to launch their own, ethnically based, political parties, last year a group formed the Kleurling Weerstandsbeweging, or Coloured Resistance Movement. But in-fighting caused this to crumble: some members wanted it to promote Goloured interests and culture; others to press for an exclusive "homeland".In fact, the coloureds’ sense of collective identity is undefined, largely imposed by apartheid’s twisted logic. They are descended from a mix of races, including the Khoi and San (two indigenous African peoples), Malay slaves imported by the Dutch, and white European settlers. And though they do indeed share much with Afrikaners-many belong to the Dutch Reformed Church and many speak Afrikaans-others speak English or are Muslim or worship spirits.Under apartheid, being Coloured became something to try to escape from. Many tried to pass as white; some succeeded in getting "reclassified". Aspiring to whiteness and fearful of blackness, their identity is hesitant, even defensive. Many Coloureds feel most sure about what they are not: they vigorously resist any attempt to use the term "black" to embrace all nonwhite people. "My people are terrible racists, but not by choice," says Joe Marks, a Coloured member of the Western Cape parliament. "The blacks today have the political power, the whites have economic power. We just have anger. The passage mainly discloses （）
冒泡排序算法在最好的情况下的元素交换次数为【 】。
Small, pink and very ugly. Hardly the qualities of a star, but they describe the deformed mouse that was the media darling at a recent science exhibition in Beijing. With a complex tissue structure in the shape of a human ear grafted on to its back, the rosy rodent was a stunning symbol of the serious strides China is making in the field of biotechnology.China is fast applying the latest life-science techniques learned from the West m aggressively pursue genome research. It’s establishing its own centers of technical excellence to build a scientific base to compete directly with the United States and Europe. With a plentiful supply of smart young scientists at home and lots of interest abroad biotechnology is on the brink of a boom in China and in the view of foreign scientists, Beijing is playing a clever hand, maximizing the opportunities open to them.For the moment, the cooperation exists mostly with Europe and the U. S. But Asia’s other biotech leaders, Japan, Singapore and Korea, also are recognizing China’s potential as an attractive low-cost base to conduct research. These partnerships--and China’s advancement in the field of biotechnology--could help benefit the rest of Asia: China’s rapid progress in improving crop yields will address food-security concerns in the region. In addition, China is more likely to focus on developing cheap technology that its predominantly poor population--and those of other Asian countries--can afford.There remain, however, serious barriers to the development of a strong biotech industry. Among them are a poor domestic legal framework, weak enforcement of intellectual-property rights and loose adherence to international standards. China is a signatory of the International Bio Safety Protocol, which should mean adherence to global standards governing the conduct of field trims. But some observers are skeptical. "The regulations look good, but I haven’t met one scientist who believes they are being fully adhered to," says a European science analyst.If shortcuts are taken, then some of the recent scientific achievements trumpeted in the official press may never make it to market. But no matter how strict lab tests are, other problems lie in wait. For example, there is a number of tasks it would take years to fulfill in the patents office, says one lawyer, leaving innovators with little protection if they take a product to market in China. The mouse on display is most significant in that （）
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