题目内容
In July 1994, the comet(彗星) Shoemaker-Levy 9 smashed into the planet Jupiter. For the first time, humans were able to witness exactly what happens when a celestial(天空的) body collides with a planet and it quickly became clear that survival was no longer entirely a question of being the "fittest". A new factor had been introduced into evolution: the ability to survive a collision between the earth and an asteroid (小行星) or comet.To most people, the risk remains academic. With all the dangers humans face -- sickness, accidents- it is understandable that people don’t take seriously the risks posed by something that hasn’t happened for 65 million years and may not happen for another 65 million years.However, many scientists believe that collisions between the earth and celestial bodies cannot be regarded as "just another risk". The main reason for this is that no other disaster -- except perhaps a nuclear war -- has the potential to destroy human civilization completely. Even the worst floods and earthquakes affect only a very small percentage of the earth’s surface and population. But the effects of an impact caused by a celestial body of just ten kilometers in diameter would make humans extinct, along with most of the world’s other animals and plants.The danger comes from asteroids and comets which cross the earth’s orbit. Asteroids pose a greater danger because they are more numerous. Those less than 100 meters in diameter are not usually regarded as a threat bemuse most are destroyed by heat as they enter the earth’s atmosphere and so never reach the ground. It is those asteroids with diameters of one kilometer or more which pose the greatest threat. According to the passage, asteroids which can do real harm to the earth are （）.
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Directions:For Questions 6—10, you will hear a report about Valentine cards. While you listen, complete the sentences or answer the questions. Use not more than 3 words for each answer. You will hear the recording only once. Why do some people send cards to themselves on February 14
If you want to stay young, sit down and have a good think. This is the research finding of a team of Japanese doctors, who say that most of our brains are not getting enough exercise—and as a result, we are aging unnecessarily soon.Professor Taiju Matsuzawa wanted to find out why otherwise healthy farmers in northern Japan appeared to be losing their ability to think and reason at a relatively early age, and how the process of aging could be slowed down.With a team of colleagues at Tokyo National University, he set about measuring brain volumes of a thousand people of different ages and varying occupations.Computer technology enabled the researchers to obtain precise measurements of the volume of the front and side sections of the brain, which relate to intellect (智能) and emotion, and determine the human character. (The rear section of the brain, which controls functions like eating and breathing, does not contract with age, and one can continue living without intellectual or emotional faculties.)Contraction of front and side parts—as cells die off—was observed in some subjects in their thirties, but it was still not evident in some sixty- and seventy-year-olds.Matsuzawa concluded from his tests that there is a simple remedy to the contraction normally associated with age—using the head. The findings show in general terms that contraction of the brain begins sooner in people in the country than in the towns. Those least at risk, says Matsuzawa, are lawyers, followed by university professors and doctors. White collar workers doing routine work in government offices are, however, as likely to have shrinking brains as the farm worker, bus driver and shop assistant. Matsuzawa’s findings show that thinking can prevent the brain from shrinking. Blood must circulate properly in the head to supply the fresh oxygen the brain cells need. “The best way to maintain good blood circulation is through using the brain,” he says, “Think hard and engage in conversation. Don’t rely on pocket calculators.” According to the passage, which people seem to age slower than the others ？（）
What’s the biggest mistake people make
At first the company refused to purchase the equipment, but this decision was_________revised.
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