Which device can perform. para11el-to-serial and serial--to-parallel conversions_____

Which of the following statements about the standard 90 db is NOT true？

A．It suits everyone.

B．It can protect only 90 per cent of the working force.

C．It requires 16 quiet hours of rest each day for the ears to recover.

D．It can hardly be applied in reality.

uce, at the price of $15 per bushel. Which of the diagrams shows the government’s demand curve ().

A、a.

B、b.

C、c.

D、d.

E、None of these diagrams.

听力原文： Objects that are vibrating make sounds．Rhythmic sound vibrations produce sound waves which travel in every direction．The frequency of a sound is the number of waves that pass a given point each second．The more rapidly an object vibrates，the greater the frequency of sound it makes．Frequency is measured in hertz．One hertz equals one sound wave per second．The frequency of sound determines the degree of highness or lowness of the sound．A high-pitched sound has a higher frequency than a low-pitched sound．Humans hear sounds that have frequencies from about 20 hertz to 20,000 hertz。Sound with a frequency higher than 20,000 hertz is called ultrasound which is too high-pitched for humans to hear．However，many animals can hear ultra- sound．Bats can hear higher sounds than any other animal．Some can hear up to 210,000 hertz．Bats send out lots of high-pitched squeaks and then listen to the echoes bouncing off things like insects．The shorter the time interval between the squeak and the echo，the closer they are to the insect．Using sound to find or“see” things is called echolocation．Another animal that uses ultrasound is the dolphin．Dolphins can hear sounds up to about 150,000 hertz．Dolphins use sound waves to find food underwater．They make clicking sounds that hit whatever is around them and then bounce hack to the dolphins．Dolphins can send as many as 2,000 clicks per second．Dolphins' ultrasound ability is so sensitive that they can detect small fish from 10 feet away．

(30)

A．The quicker it vibrates, the greater the frequency of sound it produces.

B．The slower it vibrates, the higher the frequency of sound it produces.

C．The quicker it vibrates, the lower the frequency of sound it produces.

D．The frequency of sound it produces is not in proportion to the speed it vibrates.

Antiseptics(杀菌剂) have saved countless lives, but they are most effective when the bacteria they are attacking are individual cells in suspension. Once bacteria have attached themselves to solid surfaces and formed films, they are far harder to eradicate with standard disinfectants. Bacterial pollution of medical devices is a particular problem, as those devices are then used on people whose immune systems may be in less than best condition. Surgical instruments may be treated with ultraviolet light, but that is not appropriate for everything. The result is that infections arising from bacteria attached to surfaces in clinics and hospitals are reckoned to cause up to 1.4m deaths per year.

In order to develop a better method of disinfection, a team led by David Whitten of the University of New Mexico and Kirk Schanze of the University of Florida set out to design the equivalent of a mousetrap for bacteria. The device they came up with is an empty capsule five microns across. It is made of alternating layers of two polymers'(聚合体) ,one of which is positively charged, and the other negatively so. These opposite charges serve to hold the capsule together.

The polymers in question also absorb light in a way that is likely to transfer the absorbed energy to nearby oxygen molecules (氧分子) to create what is known as singlet oxygen, a particularly reactive form. of the element that would kill any bacteria inside the capsule.

To test this idea, the two researchers ran a series of experiments in which they exposed their newly built microcapsules to Pseudomonas aeruginosa, a fatal bacterium commonly, found in hospitals, and also to Cobetia marina, a bacterium that frequently adheres to ships and marine equipment, causing dirt. They found that in both cases the microcapsules attracted and captured bacteria that were nearby. After one hour of exposure to light, they report in a forthcoming issue of Applied Materials & Interfaces, the capsules killed more than 95% of the bacteria used in the study.

What kills the bacteria is clear: it is the singlet oxygen. What is attracting them into the microcapsules, though, is not well understood. The researchers infer that the positive electric charge may have the function of attracting bacteria, since many bacteria are negatively charged and would thus be attracted to the polymer in question. Alternatively, because both bacteria and polymers are repelled by water they may be pushed together by this joint repulsion. However it works, the result is what Dr. Whitten describes as a micro-sized Roach Motel ("Bacteria check in, but they don't check out"). If the idea can be scaled up, it may prove a useful weapon in the fight against hospital-caused infection and marine-dirt alike.

According to the passage, the antiseptics will be less effective when ______.

A．the bacteria are floating in individual cells

B．the bacteria pollute the medical devices in the hospital

C．the bacteria adhere to solid surfaces, wrapped by films

D．the disinfectants are not so standard

End Your Back Pain

Like an expensive but temperamental sports car, the human spin is beautifully designed and maddeningly unreliable. If you are a living, breathing human being, you have probably suffered the agony of back pain. And as long as people continue to lead overweight, sedentary and stressful lives, the number of sufferers is unlikely to go anywhere other than up.

As it does, armies of new back-pain sufferers, many desperate and even disabled, will seek relief. When they do, they'll quickly discover just how complicated their problem really is, with its mystifying mix of physical symptoms and psychological underpinnings. The reality is that the agony will often go away on its own — impossible as that may seem when you are writhing (痛苦扭曲) on the kitchen floor. The Great Pain Mystery

Back pain can originate anywhere in the elaborate spinal architecture. Degenerated discs (椎间盘), which many lead to herniation (突出) and compressed nerves, are a common problem. Then there those wrenching pain provoked by muscle injuries, which can drop grown men to the floor. What's most mysterious about back problems is the frequent disconnect between anatomical defects and pain. Unlike blood pressure and cholesterol (胆固醇), which could be measured with arm cuffs and blood tests, lower-back pain has no objective way — the volume of tears？ the intensity of a grimace？ — to be gauged.

Many times, the precise cause of pain remains unknown. Imaging tests found that two people with herniated discs can lead radically different lives: One spends his days popping painkillers, the other waltzes through life. In a well-known study, researchers checked 98 healthy people: Two-thirds had abnormal discs even though none complained of pain. The real issue is why some people have a mild backache and some have really crippling pain. In another research, experts compared a group of patients who reported back pain with a control group who did not. Close to two-thirds if the pain patients had cracks in their discs, so-called high-intensity zones, or HIZs. But so did 24 percent of the non-complainers.

The answer has as much to do with the mind as with the body. In the HIZ study, the best predictor of pain was not how bad the defect looked, but the patient's psychological distress. Depression and anxiety have long been linked to pain; a recent Canadian study found that people who suffer from severe depression are four times more likely to develop intense or disabling neck or low-back pain. At New York's Hospital for Special Surgery, psychiatrist Gregory Lutz says he often sees men who have two things in common: crippling sciatica (坐骨神经痛) and an upcoming wedding date. The problem in their back, possibly a degenerated or herniated disc, likely already existed, says Dr. Lutz, but was intensified by the pre-marriage jitters.

Spine Surgery Breakthrough

Pain is pain, and many want a quick fix and that means surgery. Spinal-fusion surgery, one of the most invasive and costly forms of therapy (about ＄42,000) has more than doubled in the US since 1993, to about 350,000 in 2003. Discectomy, which is done less invasively, has also spiked to 342,000 surgeries per year. But these procedures don't work for everyone.

The increase in all spinal surgery has been promoted in part by technical advances promising better outcomes. Perhaps the most intriguing new development is the artificial cobalt-chrome disc. In October 2004, the US Food and Drug Administration (FDA) approved the first such disc, the Charite, for patients with degenerative disc disease. The three-piece device has a sliding medical-grade plastic core sandwiched between two metal plates, which allows the spine to move. It is believed that, such discs, like knee replacements, will give patients more mobility than traditional fusion surgery. And they will get out of bed a lot sooner too. The key is to be v

A．plain ageing

B．spine defects

C．surgical failures

D．mental stress

Internet

Almost everyone with or without a computer is aware of the latest technological revolution destined to change forever the way in which humans communicate, namely, the Information Superhighway, best exemplified by the ubiquitous Internet. Already, millions of people around the world are linked by computer simply by having a modem and an address on the "Net", in much the same way that owning a telephone links us to almost anyone who pays a phone bill. In fact, since the computer connections are made via the phone line, the Internet can be envisaged as a network of visual telephone links.

The World Wide Web, an enormous collection of Internet addresses or sites, all of which can be accessed for information, has been mainly responsible for the increase in interest in the Internet in the 1990s. Before the World Wide Web, the "Net" was comparable to an integrated collection of computerized typewriters, but the introduction of the "Web" in 1990 allowed not only text links to be made but also graphs, images and even video.

A Web site consists of a "home page", the first screen of a particular site on the computer to which you are connected, from where access can be headed to other subject related "pages" (or screens)at the site and on thousands of other computers all over the world. This is achieved by a process called "hypertext". By clicking with a mouse device on various parts of the screen, a person connected to the "Net" can go traveling, or "surfing" through a web of pages to locate whatever information required.

Anyone can set up a site, promoting your club, your institution, your company's products or simply yourself. And what is more, information on the Internet is not owned or controlled by any organization. It is, perhaps, true to say that no one and therefore everyone owns the "Net". Because of the relative freedom of access to information, the Internet has often been criticized by the media as a potentially hazardous tool in the hands of young computer users. This perception has proved to be largely false however, and the vast majority of users both young and old get connected with the Internet for the dual purposes for which it was intended--discovery and delight.

Everyone is aware of the Information Superhighway.

A．Y

B．N

C．NG

waves which travel in every direction. The frequency of a sound is the number of waves that pass a given point each second. [29] The more rapid, an object vibrates, the greater the frequency of sound it makes. Frequency is measured in hertz. One hertz equals one sound wave per second. The frequency of sound determines the degree of highness or lowness of the sound. A high-pitched sound has a higher frequency than a low-pitched sound. [30] Humans hear sounds that have frequencies from about 20 hertz to 20,000 hertz. Sound with a frequency higher than 20,000 hertz is called ultrasound which is too high-pitched for humans to hear. However, many animals can hear ultra sound. Bats can hear higher sounds than any other animal. Some can hear up to 210,000 hertz. Bats send out lots of high-pitched squeaks and then listen to the echoes bouncing off things like insects. The shorter the time interval between the squeak and the echo, the closer they are to the insect. [31]Using sound to find or "see" things is called echolocation. Another animal that uses ultrasound is the dolphin. Dolphins can hear sounds up to about 150,000 hertz. Dolphins use sound waves to find food underwater. [31] They make clicking sounds that hit whatever is around them and then bounce back to the dolphins. Dolphins can send as many as 2,000 clicks per second. Dolphins' ultrasound ability is so sensitive that they can detect small fish from l0 feet away.

(30)

A．The quicker it vibrates, the greater the frequency of sound it produces.

B．The slower it vibrates, the higher the frequency of sound it produces.

C．The quicker it vibrates, the lower the frequency of sound it produces.

D．The frequency of sound it produces is not in proportion to the speed it vibrates.

U. S. showed that regular helpings of a small portion of nuts can have a powerful protective effect against a disease that is threatening to become a global epidemic. Women who consumed a 28 gram packet of walnuts at least twice a week were 24 per cent less likely to develop type 2 diabetes than those who rarely or never ate them. Eating walnuts just two or three times a week can reduce the risk of type 2 diabetes by almost a quarter. The latest findings, published in the Journal of Nutrition, are not the first to highlight the anti-diabetic effects of walnuts, with earlier research showing similar benefits. However, this is thought to be one of the largest studies to fmd regularly snacldng on them can help prevent the condition. Although the latest research was carried out on female nurses, its likely that the same benefits apply to men. According to the charity Diabetes UK, at the current rate of increase, the numbers affected by type 2 diabetes in the UK will rise from around 2.5 million currently to four million by 2025 and five million by 2030. Left untreated, it can raise the risk of heart attacks, blindness and amputation (截肢). Being overweight, physically inactive and having a poor diet are major risk factors for the disease. Scientists at the Harvard School of Public Health in Boston, U. S. , tracked 137,893 nurses aged from 35 to 77 over a ten year period to see how many developed type 2 diabetes. Their dietary habits were closely monitored, including details on how often they ate nuts, particularly walnuts. After allowing for body fat and weight, the researchers found eating walnuts one to three times a month reduced the risk by four per cent, once a week by 13 per cent and at least twice a week by 24 per cent. In a report on the fmdiugs the researchers said: "These results suggest higher walnut consumption is associated with a significantly lower risk of type 2 diabetes in women: " Walnuts are rich in healthy fatty acids(脂肪酸)which have been shown to reduce inflammation (炎症) in the body and protect against heart disease, cancer and arthritis(关节炎). Last year, experts at the University of California Los Angeles also found young men in their twenties and thirties who ate walnuts every day increased their sperm count and boosted their fertility. The research comes just after a Louisiana State University study which showed that eating nuts can reduce peoples risk of obesity. The study found that those who consumed varieties such as almonds and pistachios(开心果) demonstrated a lower body weight, body mass index (BMI) and waist circumference compared to non-consumers. They were also at lower risk of developing heart disease, type 2 diabetes and metabolic syndrome. According to the passage, what does "a global epidemic" (Line 3, Para. 1 ) refer to？

A.A disease.

B.Type 2 diabetes.

C.Cancer.

D.Obesity.

Landfills

You have just finished your meal at a fast food restaurant and you throw your uneaten food, food wrappers, drink cups, utensils and napkins into the trash can. You don't think about that waste again. On trash pickup day in your neighborhood, you push your can out to the curb, and workers dump the contents into a big truck and haul it away. You don't have to think about that waste again, either. But maybe you have wondered, as you watch the trash truck pull away, just where that garbage ends up.

Americans generate trash at an astonishing rate of four pounds per day per person; which translates to 600,000 tons per day or 210 million tons per year! This is almost twice as much trash per person as most other major countries. What happens to this trash？ Some gets recycled (回收利用) or recovered and some is burned, but the majority is buried in landfills.

How Much Trash Is Generated？

Of the 210 million tons of trash, or solid waste, generated in the United States annually, about 56 million tons, or 27 percent, is either recycled (glass, paper products, plastic, metals) or composted (做成堆肥) (yard waste). The remaining trash, which is mostly unredeemable, is discarded.

How Is Trash Disposed Of？

The trash production in the United States has almost tripled since 1960. This trash is handled in various ways. About 27 percent of the trash is recycled or composted, 16 percent is burned and 57 percent is buried in landfills. The amount of trash buried in landfills has doubled since 1960. The United States ranks somewhere in the middle of the major countries (United Kingdom, Canada, Germany, France and Japan) in landfill disposal. The United Kingdom ranks highest, burying about 90 percent of its solid waste in landfills.

There Are Two Ways to Bury Trash:

Dump-an open hole in the ground where trash is buried and that is full of various animals (rats, mice, birds). (This is most people's idea of a landfill!)

Landfill-carefully designed structure built into or on top of the ground in which trash is isolated from the surrounding environment (groundwater, air, rain). This isolation is accomplished with a bottom liner and daily covering of soil.

Sanitary landfill-landfill that uses a clay liner to isolate the trash from the environment.

Municipal solid waste (MSW) landfill-landfill that uses a synthetic (plastic) liner to isolate the trash from the environment.

The purpose of a landfill is to bury the trash in such a way that it will be isolated from groundwater, will be kept dry and will not be in contact with air. Under these conditions, trash will not decompose(腐烂)much. A landfill is not like a compost pile, where the purpose is to bury trash in such a way that it will decompose quickly. Proposing the Landfill

For a landfill to be built, the operators have to make sure that they follow certain steps. In most parts of the world, there are regulations that govern where a landfill can be placed and how it can operate. The whole process begins with someone proposing the landfill.

In the United States, taking care of trash and building landfills are local governments' responsibilities. Before a city or other authority can build a landfill, an environmental impact study, must be done on the proposed site to determine:

the area of land necessary for the landfill

the composition of the underlying soil and bedrock

the flow of surface water over the site

the impact of the proposed landfill on the local environment and wildlife

the historical value of the proposed site

Building the Landfill

Once the environmental impact study is complete, the permits are granted and the funds have been raised, then construction begins. First, access roa

A．Y

B．N

C．NG

听力原文： University teaching in the United Kingdom is very different at both undergraduate and graduate levels from that of many overseas countries.

An undergraduate course consists of a series of lectures, seminars and tutorials and, in science and engineering, laboratory classes, which in total accounts for about 15 hours per week. Arts students may well find that their official contact with teachers is less than this average, while science and engineering students may expect to be timetabled for up to 20 hours per week. Students studying for a particular degree will take a series of lecture courses which run in parallel at a fixed time in each week and may last one academic term or the whole year. Associated with each lecture course are seminars, tutorials and laboratory classes which draw upon, analyze, illustrate or amplify the topics presented in the lectures. Lecture classes can vary in size from 20 to 200 although larger size lectures tend to decrease as students progress into the second and third year and more options become available. Seminars and tutorials are on the whole much smaller than lecture classes and in some departments can be on a one-to-one basis (that is one member of staff to one student). Students are normally expected to prepare work in advance for seminars and tutorials and this can take the form. of researching a topic for discussion, by writing essays or by solving problems. Lectures, seminars and tutorials are all one hour in length, while laboratory classes usually last either 2 or 3 hours. Much emphasis is put on how to spend as much time if not more studying by themselves as being taught. In the UK it is still common for people to say that they are "reading" for a degree! Each student has a tutor whom they can consult on any matter whether academic or personal. Although the tutor will help, motivation for study is expected to come from the student.

(33)

A．Less than 15 hours.

B．15 Hours on average.

C．Up to 20 hours.

D．30 hours at most.

nds into space. It turns out that the ionosphere (电离层), the layer of electrically charged particles that comprises the outer atmosphere, is thinner than expected-and cooler.

Understanding the shape and size of the ionosphere is an important first step in figuring out how particularly dense regions within it may distort radio, radar and navigation signals. Such distortions can make communications and satellite-based systems less reliable.

"In order to predict how severe those distortions will be, it's necessary to know how big those structures in the ionosphere are and where they exist," Roderick Hellis, with the Space sciences Center at the University of Texas in Dallas, told Discovery News.

Hellis and his colleagues have been using a suite of NASA instruments called CINDI, which fly on the U.S. Air Force Communication/Navigation Outage Forecast System (C/NOFS) satellite between 250 miles and 530 miles around the planet's equator.

The researchers never expected to encounter the edge of Earth's ionosphere at those altitudes, but that is exactly what happened during the summer of 2008, a time when the solar activity was unusually weak.

"It was a real combination of low solar activity and the satellite's range," Hellis said. "We didn't expect to be able to look at the top of the ionosphere in all places." Computer models based on previous research had predicted the ionosphere to be about 370 miles above Earth at night and about 620 miles up during the day--the variation due to temperature and other factors.

Instead, the CINDI team discovered that the transition between the ionosphere and space was about 250 miles above Earth at night and about 500 miles up during the day.

The ionosphere is primarily caused by extreme ultraviolet energy from the sun.

"It's powerful enough that those photons (光子) can ionize (使……电离) atoms in Earth's upper atmosphere," said David Hathaway, a solar physicist at NASA's Marshall Space Flight Center in Huntsville, Ala. "When you have a geomagnetic disturbance or a solar flare going off, you can get an ionosphere that is uneven, which can cause problems with radio signals and GPS satellite signals, which have to pass through."

The findings were presented at the annual American Geophysical Union conference in San Francisco last month.

CINDI is an acronym for Coupled Ion Neutral Dynamics Investigation. The device works by separately measuring ionized and neutral particles at altitudes where the Air Force satellite flies. A similar device is on another polar-orbiting Air Force spacecraft.

The researchers hope to keep using CINDI as solar activity picks up in the sun's new 11-year cycle. The next solar maximum is expected in late 2011 or 2012.

We have always had a misconception about______.

A．how far away the upper edge of the ionosphere is

B．how many particles comprise the ionosphere

C．how long the ionosphere has been existing

D．how the ionosphere extends into space