大学英语六级-90及答案解析.doc
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1、大学英语六级-90 及答案解析(总分:543.00,做题时间:90 分钟)一、BPart Writing(总题数:1,分数:106.00)1.1. 出国留学的好处;2. 出国留学的弊端;3. 结论和你的观点。BThe Advantages and Disadvantages of Studying Abroad/B(分数:106.00)_二、BPart Reading (总题数:1,分数:10.00)BAliens/BAre there other forms of life in the universe? The scientific search for extraterrestrial
2、 (ET) life forms has been bolstered by two recent discoveries. First, the discovery of life forms in exotic environments on Earth indicates that life is very hearty and can adapt to the strangest and most hostile environments. Second, astronomers found planets orbiting stars besides our sunover 50 e
3、xtrasolar planets have been discovered as of 2001. Are there alien life forms on any of these planets?If alien life does exist, what might it be like? Would it be simple forms of life such as bacteria, viruses or algae, or more advanced, multi-cellular creatures, perhaps even intelligent beings? Wou
4、ld aliens be animals, plants or have characteristics of both? Would they have arms and legs and walk upright as we do? Would they depend upon vision as their primary sense or use another way to gather information about their surroundings? Would they “breathe“ oxygen or some other gas? BGreetings, Ca
5、rbon-based Bipeds(两足动物) !/BMost of us picture alien life the way its portrayed in movies, where aliens are commonly depicted as human-like forms because they use actors either to play the roles directly in make up or to be models for computer-generated animation. Also, audiences relate to human-like
6、 aliens better than to more exotic, monster like. However, the human body plan bilateral symmetry with onehead, two legs and two armsstems from when early animals such as lizard, crocodile, or dinosaur colonized the Earths land masses, and it seems unlikely that such a shape would evolve on an alien
7、 world. So, lets forget Hollywood for the moment and look closely at the real science of astrobiology.Astrobiology is the scientific study of life in the universe. Astrobiologists seek to understand (among other things) how life arose and evolved on Earth, what governs the way life is organized and
8、what makes a planet habitable.Astrobiology combines the disciplines of biology, chemistry, physics, geology and astronomy. Often, astrobiologists must use the information learned about life on Earth as a guide for studying life elsewhere. Lets examine some of the unusual things that we have learned
9、from life on Earth: BLife in the Extreme/BUp until about 30 years ago, it was believed that all life on Earth was dependent upon energy from the sun. Furthermore, it was thought that you would probably not find life where temperatures were extremely hot, like in geysers or hot springs, or extremely
10、cold, like in the Antarctic desert.These ideas changed when oceanographers explored hydrothermal vents, openings in the ocean floor where extremely hot, mineral-rich water erupts from the crust. Hydrothermal vents are located several miles below the surface, on the ocean floor, where the surrounding
11、 water is at or near freezing, it is absolutely dark and the pressure is high. In organized communities around the bases of these vents, called black smokers, scientists found clams, crabs and exotic, giant tubeworms measuring 6 feet (2 meters) long. The water coming out of these vents is 230 to 662
12、 degrees Fahrenheit (110 to 350 degrees Celsius).How can these animals survive so far from the sunlight, under these extreme conditions? In the water, scientists found species of bacteria that split hydrogen sulfide(硫化物)from the water to get energy to make organic compounds. The tubeworms have bacte
13、ria in their tissues that help them derive energy from the water. The clams feed on the bacteria, and the crabs feed on the tubeworms.The discovery of hydrothermal-vent communities showed that it is possible for life to evolve in places without light from the sun, and in other worlds without suffici
14、ent light from the parent star. In view of the discovery of hydrothermal vents, it may be possible that life exists on Europa, an icy moon of Jupiter, which scientists believe has a water ocean beneath its icy crust.Life has been found in other extreme environments as well. Scientists discovered mic
15、rocolonies of lichens (地衣)called cryptoendoliths in rock samples of the Antarctic desert, where temperatures often drop to 100 degrees below zero and there is little or no liquid water. In contrast, thermophilic (heat-loving) bacteria have been found in hot springs where temperatures exceed the boil
16、ing point of water.If life can evolve in extreme environments on Earth, it seems possible that life may exist in the extreme environments of other worlds such as mars.BSpeculation: What Might Aliens be Like?/BSince no extraterrestrial life forms have been conclusively discovered, alien physiology li
17、es in the realm of our imagination. Science-fiction authors, especially the “hard“ ones who try to adhere strictly to real science, have been doing this for years. They first design or build a world, carefully working out its physical, astronomical and ecological characteristics. Next, they work out
18、 what type of aliens could exist in that world. An example of one such world-building exercise can be found at the Epona Project, where several science-fiction writers came together to create a world called Epona, complete with planetary, geological and ecological data. One artist, Steven Hanly, cre
19、ated Epona creatures.For his novel “Mission of Gravity,“ Hal Clement created a world called Mesklin that circles a double star. Mesklin rotates once every eighteen minutes and has a flattened shape caused by its rotation. The gravity of Mesklin ranges from three times Earths gravity, at the equator,
20、 to seven hundred times at the poles. Mesklin has a hydrogen atmosphere and methane(甲烷)oceans. Mesklinites, one of the planets life forms, are small, centipede-like creatures made of an insect skeletal protein called chitin. They have 18 pairs of legs that end in sucker-like feet, forward pinchers f
21、or grasping, a strong circulatory system and absorb hydrogen right through their shells. They are immensely stronga result of living on a high-gravity world, yet they have a fear of being picked up because a fall from a small height could be fatal on such high gravity.Previously weve envisioned an a
22、lien world and alien life forms. In our world, the planet orbits a bright star. Only 10 percent of the world is covered with surface water, but throughout the land mass there are pockets of water that collect under the sands from the sparse rainfall. The enyironment is hot and arid and the sunshine
23、is bright. The planet is massive and has gravity that is one-hundred times stronger than that of Earth. The atmosphere is an Earth-like air mixture of helium, oxygen and carbon dioxide.The two alien life forms that we envision for this world are animalsmobile predators that live around the planets f
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