题目内容
听力原文：W: Hello？
M: Hi, Amy. This is Bill Johns.
W: Oh hi, Bill. You weren't in engineering class today, weren't you？
M: I have the flu. I was wondering if you could tell me what went on.
W: Actually we had an interesting class. Dr. Collin talked about a new type of fuel.
M: Oh, yeah？
W: Uhhum, It's called Dimethyl ether or DME.
M: Oh, I remember reading something about DME. It's mostly used in spray cans,, right？
W: Right, DME doesn't destroy the ozone, so it is environmental friendly.
M: But doesn't DME pollute the air if it's burned in an engine？
W: Dr. Collin said something about its exhaust being dean, that it doesn't re lease as much pollutant as diesel fuel. And he mentioned something about DME being more efficient than other alternative fuels.
M: When will it replace diesel fuel？
W: Not for a while. It's not economical to massproduce.
M: Well, thanks for the information. I guess I won't need to borrow your notes.
W: Well, maybe you should look at them. We are having a test next week.
M: Okay, could you give them to Mike Andrews？ I think he is in your psychology class. He is my roommate.
W: Sure. I hope you're feeling better soon.
M: Thanks. Me too. Bye!
W: Bye!
(20)
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When the acidity insists on dropping, many creatures in the lakes and ponds will become affected.
ACID RAIN: What's the Solution？
One of the wildest regions in the U.S., far from civilization, is the Adirondack area of northern New York State. For years this isolated spot has had the reputation of being one of best fishing spots in the U.S.
As a boy 30 years ago, Bill Marleau first through the Adirondack wilderness near his small cabin on Woods Lake. Thousands of sportsmen have stayed at his father's lodge nearby.
But now Bill's 134 hectares (335 acres) of lakefront land have only scenic value. Gone are those huge trout that used to swim in the turbulent, nutrientrich water a short distance from his doorstep. Gone from the cool nights are the sounds of thousands of frogs and toads.
And gone are the birds that once fed on those water creatures.
Occasionally Bill sees a lone fisherman fruitlessly cast his bait into the empty waters of old lake. "I just don't have the heart to tell," he said. "This old lake's dead. It was killed years ago by acid rain." What is acid rain？
Acid rain is a popular term for precipitation in the form. of rain, sleet, snow or hail that is more acidic than normal. Acid rain is produced when atmospheric moisture combines with pollutants from power plants, factories and automobiles.
When fossil fuels such as coal and oil are burned, sulfur dioxide and nitrogen dioxide are produced. These two gases react with the water and oxygen in the atmosphere to form. droplets of weak sulfur and nitric acid.
Carried by prevailing winds and weather conditions, clouds containing these droplets travel hundreds, sometimes thousands, of kilometers from the source of the pollutants. Recently scientists found that acid rain now affects huge areas of the North Hemisphere.
Power plants and factories in the heavily industrialized regions of Ohio and Indiana are believed to be the source of the acid rain that killed Woods Lake along with hundreds of others in New York State and eastern Canada. Acid haze over Alaska is believed to come all the way from Japan. And precipitation as acid as vinegar that falls on Scotland and Scandinavia probably originates in England.
How Acidity Is Measured
Scientists measure the acidity of rain in pH units. A pH scale from 0 to 14 is used. Depending upon its chemical composition, a solution is either acidic, alkaline (basic), or neutral. Distilled water, which has a pH of 7, is neutral. Substance with pH values less than 7 are acidic, while those over 7 are alkaline.
Normal rain water with a pH of 5.6 is slightly acidic. But after reacting with industrial pollutants, particularly sulfur dioxide, the pH of rain quickly drops.
When acid rain falls to Earth, much of it ends up in lakes and ponds. In addition to failing directly into a lake, acid rains runs off land into streams and rivers that eventually flow into lakes and ponds. Once acid rain gets into them, its effects can be deadly.
Studies started in 1975 in the Adirondacks indicate that salamanders and frogs are the first to die when the pH is lowered. Normally the pH of a lake is 8,0 slightly alkaline. When the pH drops to 7, the eggs of salamanders and frogs fail to hatch. At pH 6.6 snails begin to die.
Bacteria that decompose leaf matter die too, and the leaf matter collects on the lake bottom. As the acidity continues to drop, ail the major food chains in the lake become affected. In time all the fish die.
Eventually primitive, oxygenconsuming plants nearly choke out all other aquatic greenery. Algae and fungal growth that thrive in an acidic environment move in and cover the entire bottom of the now destroyed lake.
Looking like blue vinegar, the lake is now an entirely changed ecosystem. It contains no life expect the fungal and algal growth and a few surfacedwelling water bugs.
&n
听力原文：M: I'd like to place a situationtosituation call to Ann Arbor, please. How much would that be？
W: That's 55 cents for the first 3 minutes mad 10 cents for each additional minute.
Q: How much will the man pay for a 10minute call？
(15)
听力原文： You can tell the age of a tree by counting its rings. But these records of tree's life really say a lot more. Scientists are using tree rings to learn what's been happening on the sun's surface for the last ten thousand years. Each ring represents a year of growth. As a tree grows, it adds a layer to its trunk taking up chemical elements from the air. By looking up the dements in the rings from the given year, scientists can tell what dements were in the air that year. Dr. Stevenson is analyzing one element—earbon14 in rings from both living and dead trees. Some of the rings go back almost ten thousand years to the end of the Ice Age. When Stevenson followed the carbon14 trail back in time, he found carbonn4 levels change with the intensity of solar burning. You see the sun has cycles. Sometimes it burns fiercely and other times it is relatively calm. During the sun's violent periods, it throws off charged particles in fast moving strings called solar winds. The particles interfere with the formation of carbon14 co. Earth. When there's mom solar rand activity, less carbon14 is produced. Ten thousand years of tree fines show that the carbon 14 level rises and falls about every 420 years. The scientists concluded that the solar wind activity must fellow the same cycle.
(26)
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