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听力原文： Scientists say sharks have lived in the world's oceans for millions of years. Scientists say there are more than three hundred and fifty different kinds of sharks.
Sharks do not have bones, and a shark has an extremely good sense of smell. It can find small amounts of substances in the water, such as blood, body liquids and chemicals produced by animals. Sharks also sense electrical and magnetic power linked to nerves and muscles of living animals. These powerful senses help them find their food. Some sharks will eat just about anything. Many unusual things have been found in the stomachs of some tiger sharks. They include shoes, dogs, a cow's foot and metal protective clothing.
About forty percent of the different kinds of sharks lay eggs. The others give birth to young. Some sharks carry their young inside their bodies like humans do.
Scientists are beginning to understand the importance of sharks to humans. Medical researchers want to learn more about the shark's body defense system against disease. They know that sharks recover quickly from injuries. Sharks appear never to suffer infections, cancer or heart diseases.
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听力原文：M: Ozone is an extremely active gas comprised of three atoms of oxygen. Ozone exists naturally in the Earth's upper atmosphere, the stratosphere, where it shields the Earth from the sun's ultraviolet rays. However, ozone found close to the Earth's surface, called ground-level ozone, is a component of smog and a harmful substance.
W: What is the ground-level ozone？ Where does it come from？
M: Ground-level ozone is a colorless gas that can be found in the air we breathe. It is formed through a complex chemical reaction between volatile organic compounds and nitrogen oxides in the presence of sunlight. It is hard to be watched by eyes.
W: Who is considered most at risk from exposure to ground-level ozone？
M: Children are the most at risk from exposure to ground-level ozone: Their respiratory systems are still developing and they breathe more air per pound of body weight than adults.
W: From what you've just said, can I infer that ground-level ozone is closely related to summer, the hot days？
M: Ground-level ozone is a summer time problem; children spend most of the summer outside playing at summer camps, playgrounds, and neighborhood parks and in backyards.
W: How do I know when ground-level ozone concentrations are high？
M: Ground-level ozone concentrations tend to be especially high during summer when the weather is hot and sunny.
W: Is there any organization providing relevant information？
M: The staff from the departments concerned has developed a procedure to inform. the public about expected ground-level ozone readings. Each afternoon from May 1st through September 15th, the staff retrieve and review monitored ozone data and weather forecast information. Then they develop ground-level ozone forecasts for the following day.
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听力原文：M: Good morning, madam. Is there anything I can do for you？
W: I suppose I'd like to buy something China made as presents for my husband and daughter.
M: What about some smart ties for your husband？
W: Oh, no. I've bought one for him as birthday present last month. So I don't want to buy more.
M: What about this nice fine cotton short sleeve T-shirt？
W: That's a good idea. Could you show me some samples？
M: It's my pleasure. They're of good quality.
W: I prefer light color, medium size.
M: How about this light blue one？
W: It's really nice. How much does it cost？
M: Fifteen dollars.
W: OK! I'll take it. Could you recommend something for my daughter？
M: We've got very beautiful silk products, woolen sweaters and...
W: The woolen sweaters are not on season because it is getting warm. How much is that pink pajamas worth？ It looks fine.
M: It's fifty dollars.
W: That's too expensive. I wonder if the silk piece's color will go off.
M: As a matter of fact, all the materials here are colorfast. If you are not satisfied with the price, you can try some silk scarf. It is just 20 dollars each.
W: All right. I will buy a light blue T-shirt, and a pink silk scarf.
M: That amounts to 35 dollars. Please wash the silk in lukewarm soap water and rinse well. Don't rub or wring it.
W: Here is the money. Thank you.
M: You're welcome.
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M: Well, if I were you, I'd call Lost-and-Found first since there must be important notes on the old one.
Q: What does the man suggest the woman to do？
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Acid Rain
What Is Acid Rain？
"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.
Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depends on many factors, including how acidic the water is, the chemistry and buffering (隔离) capacity of the soils involved, and the types offish, trees, and other living things that rely on the water.
Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry-deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acres to the acid rain, making the combination more acidic than the falling rain alone.
How Do We Measure Acid Rain？
Acid rain is measured using a scale called "pH". The lower a substance's pH, the more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the U.S. has a pH of about 4.3. Effects of Acid Rain
Acid rain causes acidification (酸化) of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Prior to failing to the Earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates contribute to visibility degradation and harm public health.
What Society Can Do About Deposition？
There are several ways to reduce acid deposition, ranging from societal changes to individual action.
•Understand Acid Deposition's Causes and Effects
To understand acid deposition's causes and effects and track changes in the environment, scientists from EPA, state governments, and academies study acidification processes. They collect air and water samples and measure them for various characteristics like pH and chemical composition, and they research the effects of acid deposition on human-made materials such as marble and bronze. Finally, scientists work to understand the effects of sulfur dioxide (SO2) and nitrogen oxides (NOx)—the pollutants that cause acid deposition and fine particles—on human health.
To solve the acid rain problem, people need to understand how acid rain causes damage to the environment. They also need to understand what changes could be made to the air pollution sources that cause the problem. The answers to these questions help leaders make better decisions about how to control air pollution and therefore how to reduce—or even eliminate—acid rain. Since there are many solutions to the acid rain problem, leaders have a choice of which options or combinations of options arc best. The next section describes some of the steps that can be taken to reduce, or even eliminate, the acid deposition problem.
•Clean Up Smokestacks (烟囱) and Exhaust Pipes
Almost all of the electricity that powers modem life comes from burning fossil fuels like
coal, natural gas, and oil. Acid deposition is caused by two pollutants that are released into the atmosphere, or emitted, when these fuels are burned: sulfur dioxide (SO2) and nitrogen oxides (NOx).
Coal accounts for most U.S. sulfur dioxide (SO2) emissions and a large portion of NOx emissions. Su
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