[外语类试卷]大学英语六级模拟试卷483及答案与解析.doc
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1、大学英语六级模拟试卷 483及答案与解析 一、 Part I Writing (30 minutes) 1 Directions: For this part, you are allowed 30 minutes to write a short essay entitled Obtain the Information Online. You should write at least 150 words following the outline given below: 1. 随着网络的发 展,我们可以轻而易举地从网络上获取各种信息 2.如此便捷地获取信息有利也有弊 3.你的看法 Ob
2、tain the Information Online 二、 Part II Reading Comprehension (Skimming and Scanning) (15 minutes) Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions attached to the passage. For questions 1-4, mark: Y (for YES) if the statement agrees with the
3、information given in the passage; N (for NO) if the statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 1 Part Reading Comprehension (Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the pa
4、ssage quickly and answer the questions on Answer Sheet 1. For questions 1-7, choose the best answer from the four choices marked A), B), C) and D). For questions 8-10, complete the sentences with the information given in the passage. Earth Will Survive Global Warming, But Will We? The notion that hu
5、man activity, or the activity of any organism, can affect Earth on a planetary scale is still a hard one for many people to swallow. And it is this kind of disbelief that fuels much of the public skepticism surrounding global warming. A poll conducted last summer by the Pew Research Center found tha
6、t only 41 percent of Americans believe the burning of fossil fuels causes global warming. But in a meeting this week in Paris, officials from 113 nations have agreed that a highly anticipated international report will state that global warming was “very likely“ caused by human activity. The idea tha
7、t biology can alter the planet in broad and dramatic ways is widely accepted among scientists, and they point to several precedents throughout the history of life. The mighty microbes Human-caused global warming-also called “anthropogenic“ global warming-is the latest example of life altering Earth,
8、 but it is not the most dramatic. That title probably goes to the oxygenation of Earths early atmosphere by ancient microbes as they began to harness the power of sunlight through photosynthesis(光合作用 ). Humans “are having a strong effect on global geochemical cycles, but it does not compare at all t
9、o the advent of oxygenic photosynthesis,“ said Katrina Edwards, a geo-microbiologist at the University of Southern California (USC). “That was a catastrophic environmental change that occurred before 2.2 billion years ago which wreaked its full wrath on the Earth system.“ Edwards studies another way
10、 life impacts the planet in largely unseen ways. She focuses on how microbes living on the dark ocean floor transform minerals through a kind of underwater power. “These microbes are completely off radar in terms of global biogeochemical cycles,“ Edwards told Live-Science.“ We dont consider them as
11、part of the Earth system right now in our calculation about whats going on, and we dont consider them in terms of how the Earth system will move forward into the future.“ These reactions are strongly influenced by life and have been occurring for billions of years, for as long as the oceans have bee
12、n oxygenated and there have been microbes inhabiting the seafloor, Edwards said. Creating Earth On land, microbes, and in particular a form of bacteria called cyanobacteria (固氮蓝藻 ), help keep soil in place and suppress dust. “Wed certainly have more dust storms and it would not be anywhere as nice o
13、n Earth if they werent around,“ said Jayne Belnap, a researcher with the United States Geological Survey. Scientists believe the tiny life-forms performed the same roles on early Earth. “One of the big problems for geologists is that, OK, you have this big ball of rock, the soil is weathering out an
14、d you have these ferocious winds. What in the world is holding the soil in place as it weathers out of the rocks?“ Belnap said in a telephone interview. “Cyanobacteria are also credited with that function.“ The microbes anchored soil to the ground; this created habitats for land plants to evolve and
15、 eventually for us to evolve. “They literally created Earth in a sense,“ Belnap said. “Cyanobacteria are just like it,“ she continued. “Ive been telling everybody to make a small altar and offer sacrifices every night. We owe them everything.“ A snowball planet The mighty microbes also triggered sud
16、den climatic shifts similar to what humans are doing now. Recent studies suggest that the proliferation of cyanobacteria 2.3 billion years ago led to a sudden ice age and the creation of a “Snowball Earth.“ As they carry out photosynthesis, cyanobacteria break apart water and release oxygen as a was
17、te product. Oxygen is one of the most reactive elements around, and its release into the atmosphere in large amounts destroyed methane (沼气 ),a greenhouse gas that absorbed the suns energy and helped keep our planet warm. Some scientists think the disappearance of this methane blanket plunged the pla
18、net into a cold spell so severe that Earths equator was covered by a mile-thick layer of ice. Earth might still be frozen today if not for the appearance of new life forms. As organisms evolved, many developed the ability to breathe oxygen. In the process, they exhaled another greenhouse gas, Carbon
19、 dioxide, which eventually ice-out the world. That was the first biologically triggered ice age, but others followed, said Richard Kopp, a Caltech researcher who helped piece together the Snowball Earth scenario. A new leaf When trees first appeared about 380 million years ago, they also disturbed E
20、arths atmospheric balance. Unlike animals, plants breathe in carbon dioxide and expel oxygen. Trees transform some of that atmospheric carbon into lignin (木质素 )-the major constituent of wood and one of the most abundant proteins on the planet. Lignin is resistant to decay, so when a tree dies, much
21、of its carbon becomes buried instead of released back into the atmosphere as carbon dioxide. Less carbon dioxide in the atmosphere thins the blanket of gases that keeps Earth warm, and that cooling effect can trigger global cooling, possibly even an ice age. “There was some glaciation that started a
22、round that period that was driven at least in part by the evolution of land plants,“ Kopp said in a telephone interview. Trees also affected the global carbon cycle in another indirect way. As they tunnel through the ground, tree roots break down silicate rocks into sediment and soil. Silicate rock
23、contains large amounts of calcium and magnesium (镁 ). When these elements are exposed to air, they react with atmospheric carbon dioxide to form calcium carbonate (碳酸盐 ) and magnesium carbonate, compounds that are widespread on Earth. The human difference Though it might seem as if humans are mere f
24、leas along for a ride on the back of an immense animal called Earth, our intelligence, technology and sheer numbers mean our species packs a punch that can shake the world in wild ways. While we are not the first species to drastically alter our planet, our influence is unique in a number of ways, s
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